Maybe for Bosshoss it is
I'm very out of touch, but it used to be impossible for many years. Other than DW's copy* I never saw one for sale and it has still never been for sale on eBay or Discogs to this day. Facebook groups and private sales? I would not have a clue, and if there has been a quantity found, I'm unaware.
For fun here's my guess at the top 5 rarest pressings from back From The Grave 1-8. I do not include Vols 9 and 10 because there has not been sufficient time to be certain which ones are never going to turn up on those recent volumes. Acetates and tapes not allowed. I'm not buying many 45s these days so this list could be out of date, but all of these were incredibly hard to find back in the day. Much harder than the Keggs or Aztex.
1 - Just Too Much - She Gives Me Time
2 - Village Outcast - The Girl I Used To Love
3 - Hush Puppies - Hey Stop Messing Around
4 - Pseudos - It's A Long Way To Nowhere
5 - Adrian Lloyd - Lorna
Runners Up
Centrees - She's Good For Me (first version, but it's not the version on BFTG)
Gentrys - Wild
Dry Grins - She's A Drag
Sonics - Diddy Wah Diddy (with ps)
Sloths - Makin Love (with ps)
* It was either DW or TW ....(can't remember, 20 years ago!)