I've just signed up with https://www.sperlongadata.com
For up to 30 houses, or so, they charge something like 25 a month and 1 dollar a month per tenant.
Their pitch is that you can go back 6 year and 11 months to collect old debt as well a do monthly reporting. They say that as long as the debt is verifiable and a valid debt, you don't need their permission to report them for non-payment and if any tenants threaten to sue they provide a toll free number for tenants to call if they have any problem with the reporting.
I only signed up 2 weeks ago and it's taken most of that time for them to get my credentials verified with the agencies, so I haven't reported anyone yet.
This week I AM going to start notifying tenants, past and present, so that they can decide to set up a payment plan of they want to avoid being reported. I'm assuming that the letter alone will be enough for 30% of tenants to start paying little by little, but I'd be happy to report back if there's any interest.