https://www.ebay.com/itm/251555614530
https://www.ebay.com/itm/191796804772
I'm not an expert on this yet.. But my understanding is that you should over size it slightly.. So if you have a 12k unit I would go for the 1.5 ton coil. But I would also look into flat plate heat exchanges. Those can be had cheaper in some cases. As long as you have a clean water supply and from the sounds of it you will have a closed look system with bore holes..
I'm sure the others will chime in shortly