Four options:
1. Semi dry suits were developed to enable a diver to get acceptable performance from a smaller number of stock sizes (and now some companies now sell fewer stock sizes of wet suits). The seals help make up for the pumping action of a less than ideal fit. But it has it's limits.
2. A few shops will sell you a farmer John in two sizes - one for the john and a larger or smaller size for the Jacket, but that depends on their ability to get the separate pieces as the resulting mis matched pair made from the leftovers won't sell well.
3. Most shops can fit you for and order a custom wet suit. As noted above, cost is not much more than a "quality wet suit", but the cost of that level of "quality" is comparatively high and will induce wet suit sticker shock. And if you already own a wetsuit that does not fit well (which is the case here) altering the suit is a lot cheaper than buying a new suit - custom or otherwise.
4. As someone indicated above, if the alterations are not expansive, the cost of alterations is fairly low. For example, a torso that needs to be let out a few inches involves shortening and re-sewing a couple panels. Making the sleeves smaller may involve shortening the sleeve and sewing on some binding, as well as reducing the size of a panel all the way up the sleeve as well as adding some material to fill the resulting gap in the armpit.
Superior Diving Repair Inc, does good work at a reasonable price and they give you a price for a needed alteration in advance, so you can determine what the cheapest option might be (custom suit, enlarge the torso on a jacket or shorten the arms on a jacket.)
Superior Diving Repair, Inc.