I usually don't call - I e-mail them or just sign up on their website if there is somewhere to sign up. Most of the time I just attach my license & coverage area to the e-mail I send them. Sometimes they respond within a day or two, sometimes I don't hear anything for 6 months. If it's longer than 6 months, I usually just send the e-mail again.
As far as companies that are not nationwide, try their website - it usually says somewhere in their bio page 'nation-wide agent network' or something similar. If they are not nationwide, they usually have their coverage area. If you can't find anything, contact them - it only takes a couple of minutes to send an e-mail.
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If there was a better way to go then it would find me
I can't help it, the road just rolls out behind me