After much work I feel this now deserves it's own thread.
This is a HUGE collection of track icons taken from the work done by strangedogs in the guitar icon thread and also from icon collections I have found on the REAPER stash.
The icons are all sorted into relevant folders as categories like guitars - electric, keys, drums, etc.
The collection can be found spread across these four files:
https://stash.reaper.fm/theme/583/SD%...ck%20Icons%201
https://stash.reaper.fm/theme/584/SD%...ck%20Icons%202
https://stash.reaper.fm/theme/587/SD%...ck%20Icons%203
https://stash.reaper.fm/theme/588/SD%...ck%20Icons%204
Simply unzip each file to "AppData > Roaming > REAPER > Data > track_icons" (windows 7). You can also delete all the original REAPER icons already in there as they are now sorted into the relevant folders.
ENJOY!