I replied to this on the other forum that Heavy duty inner tubes can be bought in Thailand from:
Big Bendum, 481 Santiphab Road, Tel: 02-222-7535 or Dumrong Yang Yont, 453 Maitrichit Road, Tel: 02-222-3789.
For Big Bendum you can also try Khun Pairoj Thanundonsu at Ek Paiboon Yangyont, Wongwieng 22, Pomprab, Bangkok, Office hour is 8.00 AM - 18.00 PM Monday - Saturday and Phone # 02-623-0775, 02-623-0776, Email toger05@yahoo.com
Reading the forums it seems that the 17 inch size seems to be very difficult to get hold of and at ADV Rider they advise to use the 18 inch instead - see Why are 17" H/D tubes so hard to get? - ADVrider. Nat at the Piston Shop here in Chiangmai may have them (the 18 inch heavy duty inner tubes)
I'm back in London right now and have had a pair of 21" and 18" Mefo heavy duty tubes delivered from Zen Overland. Just had a look and 17" are available. Maybe somewhere to look in future if anyone is having problems locating this size. BTW the tubes look tough and are very heavy!
Lone Rider - As I was writing on the other forum Big Bendum in BKK sold me one innetube they said was very thick and heavy duty for sure - but it turned out to be just a ordinary piece of rubber. They even made me go twice to the bank to pay it as the price we agreed upon whe I ordered was not right according to them. So I had to go another time to the bank and pay more to get it sent to CM. Called them another time when the shitty rubber arrived and asked why they sent this and the just said sorry cannot get heavy duty innertubes in Thaland. Bastards!
I tried to call the other shop you mentioned - and a least those guys were honest and told me the didnt have any and that they couldnt get any either.
So cudos to you Lone Rider for trying to help me - but it didnt work out this time.
Nat as Piston Shop do have heavy duty innertubes at the size of 16', 18', 19' and 21'.
I have read mixed meanings about using a 18' tube on a 17' rim. I guess it would be ok as an emergency solution but on a more permanent base I think I rather not.
I just found out that normal inner tubes have a 1,2 to 1,4 mm wall thickness, Heavy Duty tubes are 1,9-2,0 mm and Ultra Heavy Duty is 4 mm!
I have found a "local" source for the 17" HD version and they also have UHD in 18", 19" and 21".