I know you said "locally" but if you can't find what you need you should try CoralVue's site. I've personally purchased metric plumbing parts there for my CADLights system.
https://www.coralvue.com/metric-pvc-plumbing-parts
The Marineland 300g DD is my favorite tank. We all have dreams of going-big but I'd like something that fits my home and doesn't have a huge maintenance schedule.
For my 45g I started dosing Polyplab's One. I don't follow the instructions though since that tank only has smaller SPS corals. I dose 1 cap every other day and my levels are stable at 8.5 for Alk and 440 for Calcium. I don't test for Mag.