Whether you get a fixed wing slot or not you should absolutely get a fixed wing rating added to your FAA commercial pilot license! While I was an enlisted Helicopter mechanic, I used the military flying clubs while on active duty to get trained for my commercial and instrument ratings in an airplane.
It was 25 years ago and I have no idea if there are military flying clubs that exist anymore but there are certainly local flight schools!

The "add-on" training should not be too expensive! Theoretically, you can get a commercial add on in 50 flight hours of training. The hard part is getting total fixed wing time afterwards. You could always get a flight instructor rating and teach on the side at the flying club or buy a Cessna 150. Also, if you already hold a commercial pilot license in rotorcraft, the training for a fixed wing commercial should be a tax deductible expense (check with your CPA). I have seen way too many Army helicopter pilots in the civilian world struggle to make a living flying helicopters commercially! All the best!