I got a 1/4" loc-line set (this one) but now I’m a bit stumped on where to find the correct coupler to get this connected to the air compressor hose. How do I know which kind of fitting I need to get, and where might I find it?
Bring the set to any hardware store. Should be able to find what you need.
This might work:
Dixon Valve & Coupling DCP20B Brass Air Chief Industrial Interchange Quick-Connect Air Hose Fitting, Plug, 1/4" Coupling x 1/4" NPT Female https://www.amazon.com/dp/B00835GYZO/ref=cm_sw_r_cp_apa_bHSNAbNGD5370
The fitting you need depends on what is on you use with your air compressor/hose already. If you have the common quick connect, it is more likely an industrial style (rather than automotive— they look similar but are not compatible) 1/4" nominal size.
For the locline, I’d get a 1/4"NPT female to QC-male connector, as the kit comes with a 1/4NPT male thread on one connector. You can use a male NPT and a female-female coupling to get a little more length if needed.