Constipation is not usually a problem in itself, but a symptom of another problem. Always question your husbandry again; how can it be improved. With constipation, two things to consider are dehydration (humidity and water source) and parasites. Is your snake wild caught?
During this past month of no feces, how often has it eaten; is it still active?
If your snake is still happy, alert and active, I would not be too concerned as of yet. Consider continueing the warm bathes, the mineral oil mouse is okay too (only will help if there is a hard mass of fecal material, which may not be the case.)
As far as the vet goes, either there you haven't looked hard enough, or you arn't willing to travel far enough. Call around, many vet clinics who don't see herps on a regular basis, will know of clinics that do. Also try www.arav.com and herpvetconnect.