Try Heritage Propane up in Spring Hill. (352) 587-9788. Tell them you need to replace main valve on RV Motorhome tank. They may have the qualified technicians and provide that service - they will burn off all the propane in the tank. At the same time ask them what it would cost incrementally to re-certify your tank.
Hope this helps,
Oh, check the handle on the main shutoff valve - if it is round the tank may not be re-certifiable; if it is triangular shaped it should not be a problem. I'm not 100% sure but some older tanks with the round valves/valve location on the tank were not able to be re-certified. Others may provide more accurate information.
Towr: 2007 Country Coach Allure 470 - 37 Sunset Bay Cummins 400 ISL
Toad: 2007 Jeep Grand Cherokee (yes, it has a Hemi)