White blocks for mature gas fires? What are they called and can I still buy them?

What are they called and can I still buy them?
What to use beside caulk contained by shower...
Answers:    They are call "Radiants"and i suggest you contact a company that sells Gas appliances. You will want details of the gas fire for them .
1. Make of fire
2. model number
3. Gas council number.( GC no)
All these details will be on a small metal plate somewhere on your fire.
Any cement bonds work on plastic??
I think that you are referring to white Fire Bricks. I am in principle certain that you can still acquire them. Call a Mason (brick and block layer, not a free mason).