Where get tactile keytop sticker for keyboard

I have some custom functions assigned to some keys on my keyboard.
I want to mark those keys so I don't have to look down and confirm
I'm pressing the correct key.

I figured I'd stick some blobs with a different feeling on those
keys but that wasn't very successful. Then I figured I could to use
a few braille keytop stickers for those keys.

WOW! The price for those braille stickers is so high!!! I'm in the
UK and get hits like this one which costs about 20 pounds sterling
(almost 30 dollars)!! That's just gouging.

http://www.adapt-it.org.uk/products/braille-keytop-stickers.asp

If I had to pay those crazy prices it would be cheaper to buy
another keyboard, take the key caps, bash some dents from the
inside with a hammer & nail, and put them on my keyboard. Only
trouble is I need to mess about matching the key caps.

It's got to be easier to get some cheap "bumpy stickers". Where can
I get these from in the UK without paying ridiculous prices.