Look for a Panasonic ToughBook CF-29.
They have real serial ports, can run DOS off a disk/USB/CD for programming your older DOS radios like HT1000/MT2000's but are "modern" enough to run Windows XP for legacy CPS like Astro Spectra/XTS3000, MCS2000/MTS2000 and newer CPS like Astro 25.
Make sure you get one with a hard drive or at least the caddy. The later (mk5) CF-29 is more desirable, but even a MK1 will work.
When formatting the hard drive, I'd make a small FAT32 partition for DOS based RSS, 120mb is fine. Just boot to DOS when you need to run the DOS RSS from the partition. My CF-29 mk 5 will boot from it's USB ports.
Don't overpay, a good clean one with a good screen should not be more than $125-150.