The best commercial subbing I've done has been with the fullness of time and getting to know other people. It helps that I've lived in the same area all my life though. Commercial sub work I do this way nets me a reasonable sum.
Also, another sub job I've done for several years was a shot in the dark when someone rang me via Yellow Pages. I've been doing the job nearly three years now. I've never met the guy who phoned me. We've had a few chats on the phone over the years. I just send the invoice off to him and he sends me a cheque. Sometimes it's each month. Occasionally he misses one and sends double the next time. Occasionally I end up sending two invoices at once if I've been sloppy with my paperwork. It's quite funny really. He lives about 30 miles from me. I've no idea what he looks like and vice versa. Although it's only one shop, because of the frequency it's in my top five jobs income wise.
I also do some domestic subbing too.
I never planned it this way but currently, about a fifth of my income is from subcontract work. It took off after getting a pole system though the shop job is traditional.