I have a 1965 house with a detached garage that is clad in exterior plywood with vertical 1X stock at the seems and corners. A number of the 1X stock has started to rot and will need to be replaced prior to painting this spring.

What is the best place in Houston to source exterior grade stock like this? Would it be best to use the hardie stuff you can get at Lowes or HD?

I'd just go back with whatever was there (pine?) if you aren't residing the whole garage. Local box store or something like a McCoys should be fine if we aren't talking about a large volume.

Just get some harditrim 1x material from lowes or hd.

I'd go back with LP trim rather than Hardie. Much easier to work with and install and can be found at big box stores.

Second LP. It's about all we use anymore.
McCauleys has it.

LP SmartSide...do it once..do it right.