You have several options:
1. If you are mechanically inclined and like to tinker you can fix the tubes yourself to get max capacity (29 rounds of SC)
the bottom of the control ribs can be "extended" if you have the equipment or you can smooth them out with a dremel, sanding, and polishing. Idea is to lessen the severity of the transition of the bottom of the tube where the sides are flat to where the control ribs start to come out.
You would also want to check the internal width of the tube between the control ribs. The ideal width between the control ribs is 0.740” for typ. Reloaded ammo, no narrower than 0.730”, no wider than 0.765” and keep tube square. Too narrow left to right and there is less capacity. Too wide left to right and the rounds can start to stack incorrectly and bind on each other
Grams and TTI base pads will get you the most capacity as the bottom of those pads are beveled slightly inside. Dawson BP's are not beveled at the bottom inside. Personally, I think Grams BP's are the best.
Grams and TTI spring and followers will work the best for capacity (again, I prefer Grams)
If reloading your SC rounds should not be any longer than 1.235" OAL (+/- .005"), standard 38 super at 1.225" OAL (+/- .005")
2. If you don't tinker than go buy the MBX magazines. If you don't get at least 29 rounds of SC in them contact Adrian and he will walk you through why you may not be getting that. 30 rounds of SC is possible I hear with SC in the MBX mags, seems more common with 9mm though.
good luck