Try looking up some of the old DML Flight Jacket sets; I know one of them came with jeans. The DML Detective Chow figure (sold on Monkey Depot) has them as well. It's not too pricey and you get a Chow Yun-Fat figure, so it might be worth a get. Same with DML Rick (SEAL Team SAW Gunner). All are the same pair of Jeans.
If you can find a pair, the jeans that come with some of the Power Team Elite/ World Peacekeepers figures look good and fit fairly well on a Dragon body. I can't point you to a retailer that sells them because Power Team figures are seasonal. They usually start showing up in Big Lots stores around the end of August. They go for about $10. The weapons and most of the equipment is rather toylike (though there are some jems) but the clothing is pretty good and the bodies aren't bad if you can find one without a goofy looking headsculpt. I don't know what they will release this year but of the sets that were available last year there was a Green Beret figure that had the jeans. You might be able to find a pair on eBay. Below are the jeans on a Dragon body. They're a little loose in the waist but he's not wearing a belt and I haven't washed them to see if they shrink a bit.
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