Will wait to hear what OP was asking about "rarest" 300. But, I was going with any 300 model version as "rare". If you are going to just go with model numbers then the old 'Lifeboat' 117s first folders are the rarest and most expensive.
Here is photo showing rarest 305 Clipper with the Wenger made scissors, notice how they look different and have a sawtooth edge on the scissor blade.
Here is a look at all the Clipper colors, if you look in a clipper blade well you will see some scale plastic that goes thru liner hole to hold the clipper up so you can reach the "nic's". The brown bone has a clear plastic 'holder upper'.
OK, DM this is the best I can come up with for a 307 with scale pins. It is someone else's knife, I stole the photo, I think from a SPS. The tangs are not visible but they sure look like 307s on the bolsters. I won't argue if everyone thinks they are 301's.
Here's the two versions of the 319 Ranchers. Even though the newest version has a small nail nic, they also were made by Camillus.
You know I don't have them all, in fact there are one or two in this thread I don't have. I don't intend to try to find them all. Would have liked to have got that Clipper with black sawcut scales just to have a complete set. But, I don't have a few because I thought they were too high priced. So they slipped through my fingers and I have never and likely will never see them again. If you are a hardcore collector starting out, remember that statement. 300