May I pick your brains? How to convince ad agencies to use our Recording studio

Hi fellow warriors, I am hoping to get some creative input here .. hope you don't mind my picking your brains.

I own a recording studio - we mostly record bands and solo musicians but we also connected to an ad agency and did some jobs for TV and radio ads.

Now we'd like to do a bit more of that. So here's the question I am pondering - how do I convince ad agencies to use our recording studio instead of the ones they are using now ..

A friend of mine who used to work for ad agencies said, the only way was: Finding out the name of the art buyer, mailing in a portfolio (not email), follow up on the telephone, ask for a date for a presentation or just talk, and the hope ... He said sometimes these people are in a hurry for a quick alternative to their usual studios and then they might remember having talked to you and may give you a call.

This is something I'll try - however, maybe you have some ideas I could also try?

And what would you say - start off with smaller agencies only? To get some routine on the talks? Or dive right in and contact the whales?

I also though about targeting smaller businesses who do not have an ad agency and do all their advertising on their own (only, will they be able to afford radio and TV spots at all? Probably not)

The only way I can think of finding such businesses is by google ads .. though I suspect word of mouth to be the way people find and choose a recording facility.

I'll appreciate all your comments and ideas - sometimes outsiders see so much more than me - I have gotten a bit 'blind' after ten years of doing marketing for my business ...