Hoping to avoid a trip to Home Pro. Any local shops selling these?

There are in most areas - have you looked for shops with them outside or storage tanks? A local maid or MC taxi will normally have knowledge. They will also be able to have someone install for reasonable cost.

Edit: after writing see we in Chiang Mai forum so not sure MC drivers is an option - but local knowledge is key to finding such places unless you happen to see in travels.

There is a place on the north side of the inner moat - before Chiang Puek Gate

Up from Riders Corner about 100 meters, inside of moat, you will see a lot of water tanks there. Owner speaks English, they install and service.