Yup, they look like generic cheap 'firestick' tips. I presume they're either friction-fit or are held in with a screw through the side of the barrel?
That style of iron is sold in hardware stores everywhere, so you may be able to find tips there. Depending on who made the iron (or who they copied!), they came in a bunch of different diameters (including some very similar sizes e.g. 2.9mm, 3mm, 3.2mm, 1/4", etc). Without any sort of idea of who made it you'll have to measure carefully and maybe take a punt on what will suit.
Failing that,
this might give you some ideas for further searching.
(I've got some old unused Weller bevel tips of about the right size and in their original packaging ... um, somewhere. I'll try and find them over the weekend and pass on any details.)