Sorry, gas tank caps were dropped by Honda almost 2 years ago. If any Web site e.g., Partzilla, shows they are available, this only means that their site isn't receiving active updates from Honda. If they indicate that they have one i.e., they show a price, and you order it, you'll end up getting a 'no longer available' email at sometime in the future so, don't waste your time.
Western Honda's site shows this part as 'Call for Price', which is 'Honda speak' for, "We don't make it anymore."
If you need a cap, your best bet is to pick up a used one on eBay (or from a member) and clean it. They're very simple in design, clean up very well and can last forever unless damaged. Remove and toss the rubber gasket as they're still available from
Honda for just over a buck so, buy a few. Soak the cap in vinegar for a few days to dissolve any rust and goo restricting the vent, spring etc. Change the vinegar every day to keep it fresh. Thoroughly clean it, make sure the vent is clear and install your new gasket.
I know of no cross-over fuel cap that will work for these tanks. Our Cross-Over Parts list doesn't show anything as well.
Over the last year, I've noticed that DSS, along with their "Genuine Parts", are also showing identical "OEM Remplacment" parts. I contacted them and asked for their meaning/definition of the 'OEM Replacements' description. They responded saying that they have been negotiating with former Honda parts makers to re-produce original parts. Personally, I thought this was big news. I gave them a list of parts (including gas caps) that I thought would be good sellers. Maybe if we all contacted them with our recommendations as well, it might give them more reason to pursue additional parts that we all need.