Hmm, that's my defender resto...I really have to find time to finish that someday!
I found the clear buttons on a generic cocktail cabinet, it had the red green blue and clear.
As for those white ones, I've come across a couple before on conversions. I always assumed they were an el-cheapo replacement button, since they seemed of poor quality (soft maybe?). But they may well be pinball buttons. I seem to recall I din't like them, were the edges sharper than regular buttons???