I posted earlier, thinking my Trumpeter M983 decals were a problem. I've since established that someone spilled decal solvent all over the sheet.

They seemed wrecked and spraying them with decal repair fluid hasn't worked.

Emails to Trumpeter re buying a replacement decal sheet have gone unanswered.

Can anybody offer useful advice?

Trumpeter have is own store for spare parts on Aliexpress.com

https://www.aliexpress.com/store/1970125

see if you can find them there,is not really user friendly to find what do you need but is probably the best place or you cant try contact them from aliexpress page

Thanks I tried but no luck.

What exact decals do you need? Microscale offers all types of letters and numbers in various fonts and sizes— you can go directly to thier website. Don’t overlook thier line of model railroad letters and numbers. Or you can go to Walters Model Railroad catalog, which also carries them.
VR, Russ