There are really very few things that you need to get from HTG that can't be sourced from super neutral places that would never raise an eyebrow.
Most of my stuff comes from feed stores, landscape supply, HD and Lowes. Lots of agriculture around here and quite varied. Lots of gardens also. It's a non mmj state, but the local police seem much more concerned (and rightly so), with meth than someone with a little 'patch' in the back 40.
Anyway, all I can really think of for HTG would be the tent and the lights, especially the T-5's. I use the PLL's also. I get my bulbs elsewhere (HTG does have crappy bulbs), but I haven't been able to find the same fixtures at a 'straight' source. HID's are easy, magnetic anyway, since they are common as dirt in industry. Reflectors, not so much so.
Make a list, get your $$$$ together and buy it all in one go. If you're really paranoid, take a TAXI, either to and from your car parked somewhere else, or from home.
We have one nursery here that carries FFOF @$25/bag. I make my own, with better quality and ingredients for perhaps 1/4 the cost of the FF. You might want to consider this unless a bag or 2 will take care of your needs.
Wet