Curt, try K&N under a listing for KNSD248 which was an offset TR3 air cleaner for SU H6 1.75" carbs from a Moss Triumphtune catalogue.
I use Ramflo foam filter aircleaners on the 3A in a hot dusty climate, and the carbies stay clean. These are a centred air cleaner on the carbies, but are compact and don't foul the inner guard.
Regards,
Viv