@polygon I tend to default to 123accu for this sort of thing (mainly because they sell cheap off-brand batteries with actual customer service), but I don't know if they ship outside of NL. If not, I'd probably look for a similar reputable and specialized shop locally.
If I wanted a brand-name component specifically, I'd probably look on eBay for new old stock. eBay is often a goldmine for "unavailable" components.