Hey
Don't give up, they are around though I haven't seen either collars or Caps for some time.
Attached is my set. These things take time.
Two really great places to look would be
Geoff Oldham at
https://www.milimem.com
And
James at
https://www.jsmilitaria.com/shop.html
As I have boards for Reinforcements., Mounted rifles, Corps, Infantry and Volunteers they have been very helpful filling those gaps though sometimes it just takes luck....and about 20 years it seems..
Hope this helps.
Cheers
Corey