1) Like
@RICZ (post #8), I use E0 (that's another term for ethanol-free) for winter storage. And top off with StarTron. And make sure that the tank is full (to minimize condensation).
2) Like
@toejam (post #10), I've used the free iOS and Android app Pure Gas, to search out local E0 stations.
In my area, these were limited to a few PitStop stations, but a couple of years ago a northeast convenience chain called Stewarts started selling E0, and they're all over my upstate NY area.
3) Both of those chains sell E0 only in their highest octane, so that's what I use (for storage purposes). I also fill my gas containers with E0 and StarTron. These are for my riding mower and snowblower.
(Like my current bike, the yard engines do not need high-test, but run just fine with it.)
4) I've never experienced problems with E10 when in riding season. I mean, any day trip will typically go through more than a tank, so it -- E10 -- is not just sitting around for months, waiting to separate, as would be the case with winter storage (or summer storage, in the case of the snowblower). So I only pay extra for the E0 for storage purposes (although I may have to do this several times with the bike, if I think I'm ending the season, say, in October, but then early November has some nice days).
That said,
@Dcc, your shop guy may be playing it safe ... and with good reason. There have been reports in recent years, for instance, of some Ducati plastic tanks warping because of E10 exposure. And I have a relative in the lawn care business who has to replace mower engine seals and tubing often, a change he attributes to E10; this sort of thing may have the same effect on some similar motorcycle parts, particularly with vintage bikes that don't have as chemical-resistant seals.
So, it seems that the vast majority of bikes are okay with E10, especially when it's not sitting around for long periods. The flip side is that if you want to to really CYA -- talking about ALL bikes under ALL circumstances -- your shop buddy is probably right to be cautious, because there have been some problems ... so his position covers all the bases.
5) Now, E15 is another matter entirely. As the AMA frequently points out in its magazine, web site, and emails, there are NO bikes that are designed to handle that, it will void all bike warranties, and so forth. The AMA rightfully worries that any increase in the availability of E15 will drive E0 out of the market, make even E10 harder to find, given limited pump nozzles. Just thought I'd mention E15, since we're on the subject.