How many times can workers comp. ins. request an IME exam?

There is really no limit as to the number of exams the carrier can jump you through.  Around 5 months or so between exams is not unreasonable., especially if there has been a change in your condition or significant medical services requested. Likewise, if you have filed a 101 package with DWC, then you likely included a Form 107 impairment evaluation.  The insurer is within its rights to schedule an exam.