Sliding shelf for keyboard - where?

I have a PC desk that I like. It doesn't have a separate sliding shelf for the keyboard. Didn't think I'd need one, but I do now. Can I buy a DIY one? I shopped this morning but couldn't find one. Found shelves, of course, but none of the slidy-type brackets that I would need in order to fix it to the underneath of my desk. Any suggestions?

I did an eBay search for "keyboard tray desk" and it came up with a few kits that you can retrofit to an existing desk. Not sure if this search link will persist or time out but here it is anyway:

[broken link removed]

Perfect - thanks Clubman.

Saw a bunch of those "slidy" type brackets in Atlantic Liffey Valley only last week-when I was looking for something else-I guess other branches will also have them

Thanks PNH - I'll go there so.