There used to be a lot of stuff you couldn't buy at all, or had to travel abroad to get. Actually, smuggling was a national pastime.
Nowadays, it's the so-called "flat Earth", i.e. it looks as if you can buy anything anywhere... but looks can deceive. I've had a long list of stuff you can't find in the US. Now it's time for another one, what you can't buy in Serbia. This will grow much slower, because I don't visit the shops so frequently - the distances being shorter, the driver is not mandatory.
- mason jars - they seem to be typically American (as they take a lot of care to keep their masons from running freely, they want to keep a tight lid on them)
- varieties of rice - there is good Macedonian rice, and traditionally it was imported from Thailand and Pakistan (I think), but better types like jasmin, brown or shortgrained (for sushi, of course) are unknown here. Some kinds can be found in Blok 70 of Novi Beograd, which is its Chinatown.
- filters and belts for vacuum cleaners - actually, you can get them but not in retail; the repair shops sell them, so you need to keep the warranty slip with the address of your local shop, and hope that they are still in business when you need them.
- domestic industrial products, which used to be very popular years ago. Few have survived the general destruction of industry, brought by transition back into colonial capitalism, but many are gone. The list includes most of the brands of local beer, pencils from TOZ, cars (except Zastava, which is still holding, more or less), toys, children's books by local authors (all you can find are translations), chewing gum (only the aspartame-laden Orbit and a few others, the assortment at the counter is 95% the same as in your Walgreen's/Walmart/Kroger/Safeway)...
- rogač, aka carob tree, was a common ingredient in several cake recipes. Haven't seen it in decades.
- several kinds of tea, specially the rosehip tea (which was also popular in Germany - see if Hagebutten tea is still around), linden tea. They were pushed out of market by those fruit-flavored tealike beverages.
- barbecues running on gas simply don't exist; the kiosks using gas don't advertise it, but those using charcoal do.
- spades, shovels, hoes with longer handles - the local standard keeps them at 130cm, which means you have to bend while digging; also the spade which can act as a shovel doesn't exist, it's a rather flat job and the soil has to be wet enough to stick to it if you want to shovel it out, but then if it's any more wet than that, it sticks and doesn't fall off.
- pyrex measuring cups or any equivalent; there's plastic but not quite there. Took me some years to find one, and even then they had that one, of 1,5l, no other shape or size (2017).
- ćeten alva with taste of ćeten alva. There is one with vanilla taste, and possibly one more taste (chocolate, perhaps). The original is gone. Can still be found at village fairs, made by small confectioners; industry is unable to produce it.
2017: UV resistant adhesive tape. It breaks under sunshine within weeks.
2018: Parmesan or equivalent cheese. There's something of the kind, though, but under some cryptic name, I actually had to ask to be pointed to the discovery. It was a tiny bag, perhaps 20g, barely enough for a couple of plates, and tasting it didn't leave an impression. In the days of totalitarian commie villains we had half kilo bags of excellent parmesan made by Kolinska and a couple of others, even in the army.