Joe, one of the benefits of membership in the Home Orchard Society is receiving our Pome News. For years they've published each variety of scion from the last Scion Exchange; we can only hope those varieties will return.

Your desire for a later ripening apple that would pollinate your Gravenstein may be difficult. I don't know if "that's the way it is?" ...but I've found early blooming apples to also be early ripening varieties...

One of my favorite apples is Golden Delicious; they've a long bloom time, a long window of "eat-ability" (crisp, to sweet), and hang on long stems for weeks. I've little problem with disease, and though you can find them in most grocery stores, home grown are always better!

We've some real connoisseurs around here, I hope they speak up!

Check out the following; though it appears as I remembered: Yellow Delicious; early blooming, yet mid-to-late season ripening. It can be pollinated by Lodi (which is basically the same apple as a "Transparent.") I'd plant a stand-alone Yellow (or Golden, same thing) Delicious, and graft a branch of Transparent / Lodi onto your Gravenstein. Transparent is an excellent pollinator for Gravenstein's.

http://www.arborday.org/treeguide/TreeDetail.cfm?ID=55 - scroll down

Rootstocks aren't my 'specialty,' I understand them - but have to look each one up. I generally go for a more vigorous rootstock than most, due to clay soil and deer problems...

And remember, you can always graft something later ripening to your Yellow Del. I think it has a long enough bloom time to cover most varieties - but do check.