SMT covered a lot in his post,
I will try to add something extra, which mod parts shops are up and running.
ModMaker UK, sells 510 connection, Evolv chipset, Yihi chipset, and MM mosfet, battery tubes, battery sledges with keystone connection, wires, magnets, and more.
Stealth Vape UK,
The main supplier for Evolv, and the one who does warranty work for Evolv in Europe.
510 connections, battery tubes, Keystone battery sledge, wires, stabwood, and a bunch of other things.
ModForge Italy, aka SteelLabs aka ModDog, legendary in the industry.
His strength is 510 connections, which are far above the competitors, battery tubes, and a little bit else too. He is also an excellent designer.
He also supplies a lot of parts for High end, TEK Division and SubMonkey are two that use 510 and batt tubes from Modforge. modforge is run by Michelle.
There are other shops, but many have closed or are small.
If on the other hand you go towards the cheaper projects, nothing wrong with that, the Chinese industry is not what it once was.
It is rare to see a Chinese vape chipset, and after FastTech closed down, even a 510 connection has become harder to find.
I have not seen Battery Tubes from China.
The Yihi Chipset is also hard to come by.
Most Chinese manufacturers do not sell chipsets in bulk that they use in the mods