How to contact a seller for carry-back financing?

[Cary Crites]

I'm looking to make a offer for seller financing, but the listing is on the MLS and I likely don't have time to send a mailer before the property is snatched up. For those of you that do this often, do you typically go through a realtor to make contact, or have another way to reach out? All I have is the owner's PO Box from the accessor's records.

Thanks in advance for your help!
Cary