OK, vi sätter punkt och avslutar här.
Jag borde ha insett att det var dödfött redan fån början.
Hav tålamod eller försök med Google 
Har googlat runt åt dig och samma fråga har tydligen frågats på många thaifora.
Tyngre pjäser (gasdrivna) som du efterlyser ser ut att vara illegala att döma efter inläggen jag hittat,
men kolla själv här eller på andra ställen, Jag googlade på "buy airguns in Thailand".
I went to a place called Saphanlek market which has the cheapest DVD's and games I have seen in Bangkok and here they have about 4 or 5 shops for guns and some mighty impressive pieces too.
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I can sell you a potato gun.
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There are 2 gun shops in Korat, that I've been to, but it's difficult to give directions. They're near the town center by the statue of that woman, who they admire.
They sell brand named airguns, but you need a licence.
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air guitars are VERY cheap here. in fact i'll sell you mine for bht 6k.
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There's a whole row of gun shops in BKK between Chinatown and Sanam Luang
Don't buy the cheap ones made here they are shite.
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From these posts and speaking with people around Udon it seems air guns or rifles are illegal, shame
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http://www.thaivisa.com/forum/topic/78959-compressed-air-gun-for-competition-shooting/
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S. SRICHAROON GUN ACCESSORIES & HOLSTERS
111, Peerapong Road, Wang Burapha Phirom, Pra Nakon, Bangkok 10200, Thailand
heading: Gunsmiths / Gun Shops | Defense & Security Suppliers
2 MHAKIMI
98 Chareonkrung Road, Near Unakan Square, Wan Burapat Area, Chinatown, Bangkok 10200, Thailand
heading: Gunsmiths / Gun Shops
3 GUN AND GUY ENTERPRISES
111/1, Chroen Khung Road, Wang Burapha Phirom, Pra Nakon, Bangkok 10200, Thailand
heading: Gunsmiths / Gun Shops
4 SUPSIRI SUPPLY LTD., PART.
94, Onnut 52, Sukhumvit 77, Suan Luang, Suan Luang, Bangkok 10250, Thailand
heading: Gunsmiths / Gun Shops
M