Is there not a single hydro or indoor growing store where you live??? (cant help as much bc idk where...) but I know you can order it on-line... like amazon. The great thing about it is that it's already ph balanced soil, no nutes needed for up to four weeks. I don't own/use a ph tester bc I use distilled water from a jug. It's already at 6.0ph... so the mix of the 2 hasnt given me any problems, haven't had to use nutes at all yet.
As far as the box... thats a good idea, but remember that you are going to have small plants for a bit, so only one box will be more than enough space right now. You can attach your tubes to the top of the box (with zip ties maybe), and you can even make a power strip assembly like the one I showed you before... that can also be zip tied to the lid... More than enough light and space for beginning vegetative growth
If you send me a private message with your whereabouts, I can try and find a place for FF for you... It's more widely available than people think it is... MG killed my first set of plants... haven't done anything different this time but the soil... and well, you have seen how nice they are...
. Just trying to decide between 250W or 400W. I'm going to go ahead and build the entire box (and remember to allow drainage this time lol). I'm just going to see where this goes with the correct pH, sufficient light, and carefully monitored nutes.