I would try to buy them online from their post office. For the USA, there is https://www.usps.com/business/postage-options.htm:
“Print Labels Online with Click-N-Ship
With your free USPS.com account, you can pay for postage and print just one label or a batch of shipping labels online”
Germany has (https://www.iamexpat.de/expat-info/germany-news/deutsche-pos...):
“You simply need to open the app, select the appropriate postage service, tick “Code for labelling” (Code zum Beschriften), and pay with PayPal. You will then immediately receive a code, consisting of the letters #PORTO and an eight-digit string, which you must write in pen in the top right-hand corner of the envelope or postcard. Then, just pop it in the post box, and you’re done! The code is valid for 14 days and can only be used for Germany-bound mail.”
That 14-day limit may not be a good idea for this use case.
In addition, the 14-day limit no longer applies. Deutsche Post were challenged in court, and the digital stamps must now last for as long as conventional stamps do:
https://nrwe.justiz.nrw.de/olgs/koeln/j2023/3_U_148_22_Urtei...
Is return postage something that, normally, my local post office would help me with? E.G. do they have some method of marking or adding post to a package that would be accepted globally (or at least within the destination country)?
I think I've sent far more international letters and parcels than domestic. Christmas cards for elderly relatives in the country I was born in, and postcards when I travelled abroad.
Some obscure things I sold on eBay were mostly sent abroad.
United Kingdom
The Royal Mail stopped selling IRCs on 31 December 2011[26] due to a lack of demand. United States
The United States Postal Service stopped selling international reply coupons on 27 January 2013.[27]
"""
https://en.wikipedia.org/wiki/International_reply_coupon#Uni...
That explains why I was confounded in my efforts to search within USPS results.
> I was disappointed to find out that the UK’s Royal Mail discontinued international reply coupons in 2011. The only alternative that I could think of was to buy some US stamps.
https://shop.post.ch/en/packing-sending/sending-letters/regi...
OP was ordering US stamps to include _in_ the letter, on an SAE (self-addressed envelope) they were sending _from_ the UK, so that the FSF could reply (from the US) using said stamps.
As a millennial myself, I have no idea where else I'd look for <recipient country> stamps should I want to include them on a SAE I was sending to said country, so that they recipient wouldn't incur the cost of replying to me.
I don't find looking on eBay particularly strange, though I'd do a quick search for alternatives first.