The farnell code for the standard switches is 914-461 (2 pounds for a pack of 10). There's a 16mm version, which makes the buttons flush with the empeg display (but still operable - just harder to find in the dark!) which is 917-450 (same price).

The clear tops are 311-2445/311-2457 respectively for short/standard length.

All on p497 of the "Electrical" (book 4) of the current catalogue.

Hugo