Rapid Air Weapons in the US ( likely everywhere they are sold ). Martin and Sandra are just top notch and have old world pride in work, airguns or other. I've met them both as well as Dottie & Son, all great folks. I had two made a .22 and a .30. Any question anytime is just fine ( and he does listen to people ).
Don't fall for the myth that RAW's are not "stocked" anywhere, Jin & Nancy are very people I've met & dealt with JJim try's to keep some thing. The RAW dealer in AZ seems to have a great inventory - not to mention knowledge , the go to guy for RAW BR, met him , fired his .357 & got all kinds of information and invites to shoot more, anytime.
I would mention Crosman but that doesn't fit the OT.
Having the owner assemble every rifle does seem to aid in QC a great deal and if you every need anything they do answer the phones.
Foreign ( to the US anyway) manufacturers using U.S Importers and or dealers would naturally have a harder time with parts ..... though just 15 or so years ago airgun dealer kept parts available for years & years and they were always easy to get from whomever you purchased from. Until about '05 I thought all airguns came shipped inside boxed a plastic case,
Now, if you might be in the UK and can walk to your local STOCKING - co0mpaired to Ace hardware here- things might be slightly different?
John