Are there good dive spots easily accessible from Kuala Lumpur, without flying?

You have a couple of options for doing this:

• Tioman Island: Very popular and consistently busy due to its how easy it is to reach from Singapore. (And thus gets a lot of weekend visitors from there.) You'll need to take a bus to Mersing to catch the ferry to Tioman. It is, however, somewhat of a touristy destination. That may be a good thing or a bad thing depending on what you like.
• Redang Island: The main access city is Kuala Terengganu, which is seven hours by bus from Kuala Lumpur. Redang is particularly famous for its white sand beaches and how clear the water is, so diving conditions are excellent. Terengganu is one of the more conservatively-Muslim areas in Malaysia so typically you wouldn't finds bars, but Redang is big-enough of a tourist destination that it does have nice bars and restaurants / cafes to relax while on the islands.
• Perhentian Islands: These were by far what I liked the most out of the ones mentioned here. They aren't that heavily-visited by tourists and hence I quite liked the vibe here. Ferries run from Kuala Besut; there are direct buses from Kuala Lumpur but they run on a reduced frequency during off season. You could also go to Kuala Terengganu instead by bus, and then hire a taxi to Kuala Besut (it's not that expensive). As for the islands themselves, the water isn't as clear as Redang but the dive sites are still quite good. More importantly, it's a major conservation site for turtles, so you can go and see breeding turtles sometimes. I also quite liked Shark Bay where you can dive along with sharks.

Buses from Kuala Lumpur should cost RM 30-40 for the cheaper companies such as Transnasional going up to RM 50-60 for the costlier companies. The time taken by the buses is the same, the difference lies in how comfortable the seats are.

Tioman island would be a good place for diving. I went there last year. It's a beautiful little island about 50km off the east coast of peninsular Malaysia.

You have to take a bus to Mersing, a port city in Johor state. From the port at Mersing you can take the ferry to Tioman.

Bus ride from KL to Mersing is about 6 hours. I found the night bus more convenient since it reaches Mersing around 5:00AM and you have first ferry in just a couple of hours later. The ferry takes about 2 hours, if I remember correctly.

I discourage going Tioman as its not spectacular and is full of people coming from Singapore to do quick dive trip weekends. It might be better during the week.

I have visited (but not dived) in the Perhentian Islands which are northeast of Kuala Lampur (KL). The beaches and scenery there are the best I've seen in Southeast Asia. There are many Dive Shops and I heard a lot of good things about the diving there. We snorkeled there and the water clarity and species diversity was incredible.

A good way to do the Perhentian in a relatively time efficient way is to take the overnight train from KL to Tanah Merah Station. You can book these tickets online and can get sleeping berths usually without trouble. You can get decent sleep in these and they're quite affordable - but in no way fancy. Once you get to Tanah Merah you can hire a taxi for the 1 hour drive to the ferry terminal at Kuala Besut. From there its a 1 hour boat ride to Perhentians. There are many diving option packages available at the tour company offices at the Kuala Besut terminal.

We did a 3 day trip with the overnight train option and didn't feel too rushed. Diving may make the trip busier though.

Its good to do a bit of research on which island you want to stay on - there is Perhentian Besar (Big Island) and Perhentian Kecil (Small Island). The big one has more resorts and the small one has more backpacker options.

Make sure at some point to go to Turtle Beach on the big island. It is the most incredible white sand beach I've been to.

Since I live here and I AM a diver, you're not in luck. There is absolutely no where to dive around here. Even if there was, the visibility would be 0.5m....

So, your best bet is to fly in from Feb-Oct, head over the the east coast islands of Tioman, Tenggol or Prehentian to do some serious diving. Tioman on the other hand seems the be the best weekend dive spot, drive there on a Friday, dive on Sat and Sun, leave after lunch and you're back in KL.

Otherwise, I would personally recommend diving in Sabah, especially Mabul Island or Sipadan Island. You can check out some of the Mabul Diving Packages too. Well, that's where I dive usually :)

All the best!