These LG/Sanyo cells are 4.35V max charge which is a little different from the typical 4.2V but you can charge them up to 4.2V and just lose out on a little bit of capacity
https://batteryhookup.com/products/3-lg-sanyo-18650-3000mah-cells-in-modem-batteries
According to HKJ (one of two battery Jesus figures in the industry) these cells handle 5A discharge just fine so if you bought several packs and put them in parallel you should have no problem. I'd do 5 packs in parallel since that would give you 25A of discharge power and roughly 15Ah of capacity. You could easily add more. The nice thing is these cells are already in series...the only catch is you really need to make sure none of the cells are seriously degraded. Voltage is going to be the first indicator but a simple discharge test can tell you a lot more...since they are already 12V you could hook up a 12V 25W lightbulb and that would be like a 2A discharge test. It should run for about an hour and 15 minutes until the pack hits 9.0V with each cell hopefully being close to each other around 3.00V
https://lygte-info.dk/review/batteries2012/LG%2018650%20D1%203000mAh%20(Pink)%20UK.html%20UK.html)
Or you can buy an Atorch DL24 for $30 off a certain chinese store and use that to do your discharge testing. Really great piece of testing equipment to have around. You can test batteries, power supplies, powerbanks, etc. Saved myself more than the $30 cost just by identifying power banks that didn't meet capacity and using it as evidence to get a refund.
I cut that up since Reddit likes to block links to that chinese store
A cheaper option for a discharger is the ZB2L3
I've used this BMS many times and it works just fine. You can find it for $4. This would limit your charging to 4.20-4.25V. Finding a BMS for 4.35V cells might be a little tougher but I'm sure they are out there.