6v Battery replacement

Batteries are like everything else right now; it's ridiculously hard to find anything to buy. I buy hundreds of Deka batteries for off grid solar system. My local Deak dealers has been having great difficulty sourcing batteries for me including 6v GC. If he happens to call the warehouse right when they get a pallet in it's fine. If it's just after the pallet sells out there's quite a wait. I've had to take some "other" brand batteries just to finish some jobs.
It's the same with trucks, bicycles, circuit breakers, PVC conduit, etc. Factories just can't keep up with the demand, particularly given all fires, freezes, tornadoes, covid, etc.
I'd absolutely go back with Deka if you can find them. Concord and Trojan would also be excellent choices.

They are not inexpensive, but they are available from Lowes.

https://www.lowes.com/pd/Deka-6-Volt-448-Amp-Golf-Cart-Battery/50183775

Whatever they have at Samsclub is what we get, current set of GC2 batteries are Duracell with 5 years on them and a good ways to go. Set we had prior from Samsclub were Interstate, still going after 8 years (tested good at Napa) but Samsclub had a ridiculous sale on our Duracells that I couldn't resist, plus they have a few more amphours.

Batteries are primarily made by a couple of manufacturers anyway, proper charging is paramount followed closely by monthly maintenance. We always keep our rigs plugged in while in storage, smart converter/inverter charger does the rest. For about the price of gas on a single RVing trip we have our batteries covered for the next 7-9 years,

According to the specs I could find, they are the same size as a standard GC2 golf cart battery.

East Penn manufactures both Deka and Duracell brand batteries.

If you are happy with the Deka batteries, why not replace with them?