There is one hardware wallet option for MAID which allows for offline keys & MAID transactions; an offline computer with Armory.
Armory addresses can be added to OMNI to perform offline Omni asset transactions.
One thing to check is whether you’ll need to use an older version of Armory to use non-segwit addresses, or whether segwit addresses work fine with Omni-armory offline transactions.
Edit: for this, a cheap windows 10 64-bit tablet will do the job, but unfortunately it won’t work on a 32-bit version of Windows.