Any advice from personal experience of which Immigration Office can/will process the extension without a TM30?

Or an agent who can orchestrate it?

Many immigration offices will require a screenshot of your TM30.

Where are you staying.

Most hotels do them and can provide you with screenshot when requested

South of Pattaya 

House in Moo Baan

 

I'm aware of the rudiments of obtaining TM30 - but for reasons of circumstance I need a work a round

Checkin at a hotel that will do a TM30, then ask for a printout of it.

Booking a cheap Hotel/Guesthouse for the night preceding your application at your local Imm Office for the 30-day extension, would be easier/cheaper than engaging an Agent. 

You do not even have to spend the night at the Hotel/Guesthouse, and might even get a huge discount when you clarify that you only need a copy of the TM-30 of you having booked a room there.