Paul,
I think you are right re a long hunt. I just scoured my ebay archive of #10 Griswolds for the last month. There were no ribbed handle #10s at all in that time. Which other rib handle Griswold skillets do you have and which are you looking for? I'll keep an eye out just in case.
The #10 you are looking for should have a heat ring, ribbed handle, and large block logo. I've seen the heat ring and ribbed handle on slant logo #10's but not on a block logo skillet. I've seen at least 2 different handle variants on #10 block logo skillets with heat rings. If there is a ribbed version, that would make 3 variations. The two variants I've seen were: a flattened place similar to the large logo smooth bottom, also a version with a small rib that extends about 1/4 inch from the side of the pan, then goes to a flat place.
I'm looking for a #10 smooth bottom large logo to complete a set from #3 through #10. I could have bought a couple the last few weeks but I'm not about to pay the "OUCH" price of $70 that they sold for.
Good luck with the search!