For fuel, I like torco, they'll ship 1 gallon for ~$60 which is as good a deal as I can find anywhere now, both their car 30% and plane 15% have been easy to tune and smooth-running.
Make sure you're not getting counterfeit OS plugs on eBay, I've tried reporting the listings I do see. They'll price them only a few cents cheaper so they show up first in listings, but they're not so cheap it's "obvious"
https://www.os-engines.co.jp/rule/kinkyuu2021_10_12e.html
The most obvious giveaway is an italicized url for the os website on the packaging.
View attachment 218732
I think some of the counterfeit sellers are getting smart about this and posting pics of all-legit glow plug packaging, then shipping the fakes. You can buy the fakes on AliExpress for $4.50 each.
I only buy glow plugs straight from brand-name retailers because of this, it's especially offensive to me that by buying the counterfeit you're also costing OS crucial ongoing sales in a very tight market, and getting an inferior product for most of the cost of the genuine article.
Glow plugs are <1% of the cost of the hobby to me, when I was running surface nitros I'd replace one every few weeks, but in planes they last months.