It is unfortunate that belts can't be ordered separately because it can become quite an expensive exercise, buying whole figures when all you need is their belts.
I once sold some Playmobil accessories which included several belt parts on eBay.
The buyer wrote to me after receiving the lot, asking me if there was a special way to put the belts on the figures!
It was wrong of me to assume that everyone knows the figures need to be taken apart first, but this was because I had been doing it so long that the process had become almost automatic.
Luckily, the buyer was able to work it out by themselves after being pointed to some web pages with disassembly instructions. *phew*
This is probably one of the reasons that Playmobil don't sell these types of parts separately.