If you're looking for a genuine Motorola VHF/UHF stubby antenna, you won't find one, because they never made such a model.
The only VHF/UHF antenna that Motorola makes is the PMAT4001, which is the standard 8.5" antenna for the APX series.
You'll either have to try to find something aftermarket, or you'll have to go with a single band antenna and compromise on the other band. Using a stubby antenna is already a compromise, so expect to have degraded performance no matter what.