I suppose it's possible he wore different boots in the earlier seasons, but I've watched seasons 1-3 for the specific purpose of looking at the pants, the boots, the watch, etc., and IMO they're the same boots throughout; these may be a carry-over from a previous Diesel boot.
The pants...yeah, I think that's going to be another tough one. I've looked at hundreds of pants online, and I haven't found any that have the pocket on only one thigh. But you know these designers--they'll do a run or two of any given product, then either discontinue it or change the design completely.
Speaking of which...does it make sense that a serial killer with in-depth knowlege of police procedures would not only use such obscure items but use them repeatedly? I mean, Dexter would know that shoes have a very distinct wear pattern that are unique to the wearer, and that if he were to accidentally leave a footprint in a location the police were investigating it could lead them right to him if he were under suspicion. And the clothes...I know he takes precautions--wears the apron, the cover sleeves, rubber gloves, etc.--but the slightest random drop of blood or tissue could wind up on any exposed part of his "kill clothes" (or in the recesses of the expandable watch band on his wristwatch, for that matter) and, again, link him directly to one of his victims. In a real-world sense, it makes more sense for him to wear readily-available clothing that could not be traced back to any particular distributor, and to destroy the clothing after the "job" is done, including the boots. Which means he'd need a new (and affordable) set of clothing for each kill; I don't think he'd choose such expensive and difficult-to-locate items. I know wardrobe designers are going for a particular look when they compile wardrobe for a particular character/actor, but sheesh!!! Sorry, rant over.