You might have to try a few places. I went looking for some truck tubes a while back and went to every tyre dealer in town. All said they are very rare now because most truck tyres are tubeless! :'(
Found a servo and they had a big pile out the back. Owner said to help myself. I found four good tubes and went to thank him. He then gave me, free of charge, valves and caps for each tube. I told him I don't mind paying, but he would not hear of it, just said to make sure we have fun.
Now that was great service.