wouldn't say rare but uncommon for sure. I've seen probably a dozen or so in the last 10 years, been a few on this site as well as over on CGN.
The .307 Win cartridge is slightly less powerful than the .308 but is handicapped somewhat by less efficient bullets. This has been mitigated by the availability of Hornady FTX bullets. If you reload, you can use .308 dies to size and seat .307 cases/bullets. The cases are slightly different in that the .307 has thicker walls and is rimmed versus the .308 being rimless. Do NOT use .308 data in the .307
Hope this helps you out in your decision making process.