I’ve not shopped with Camden Grey so I can’t vouch for them one way or the other. However there are quite a few places you can buy Oakmoss absolute and you’ll get a fair idea of what it smells like from most: you only need the top quality stuff if you are going to make a fragrance with it.
As to what to buy, certainly vintage Chypre will give you a good idea as it’s a key component of those (or was before IFRA made it so restricted that it was mostly replaced with synthetics).
But don’t neglect the Fougère category, also based on oakmoss, but in this case in combination with lavender and coumarin. In my view some of the best interpretations of oakmoss are of this type. Also don’t forget that the very first fragrance of this type Fougère Royale, was also the first perfume known to use a synthetic (the coumarin) and has a pedigree going back to 1882: they have to be worth a look IMO.