I've seen a couple conversion kits for .22LR, but nothing on a .22 Magnum conversion. A revised gas system to operate with the magnum cartridge or a magnum blow back system would have to be designed. This by itself would be cost prohibitive if not planning on producing 1,000 conversion units or so. Next the magazines would need to be modified to feed the .22 Magnum, or an adapter would need to be built.
A .22 LR conversion kit modified by reaming the barrel, and then altering the recoil system to make it magnum friendly (if it is blowback, or recoil operated a heavier recoil spring would be the first step) Next the magazine would need lengthening.
Not a good conversion for a one off, especially if you are not doing it for yourself.
A Ruger 10/22 Magnum with some aftermarket parts hung on it would be easier, and a ballistic twin.