I doubt you will find any used ones. I wouldn't trust any after market wheels here. Mostly chinese rubbish. You might be able to get something in bangkok or pattaya. postage wouldnt be too expensive and a better chance of decent aftermarket or used. Triumph has 2 or 3 factories in Thailand, so maybe you could get from there. Google triumph owners club, they might have one in thailand somewhere.
Probably better to import them or even bring them in hand luggage. i know and australian brought a complete gasgas 250 in disassembled as "sports equiment" on a plane
Best bet is probably Steve at Dynotuned on riverside, all his stuff seems to be Harleys, but you never know. Beyond that in local market, the bike shops out on st.271 south of Russian Boulevard & around the corner a bit have piles of spares & oddities, you might just get lucky, or at least find somebody who knows somebody locally.
Meum est propositum in taberna mori,
ut sint Guinness proxima morientis ori.
tunc cantabunt letius angelorum chori:
"Sit Deus propitius huic potatori."