This is my first post here so I'll try to avoid any faux pas but forgive me if there is any. My local seems to always have nothing when I'm there...
The first thing is the supplier or distributor might not have much or any stock, but I have definitely seen lots of shops getting big drops of almost all brands recently, so maybe keep an eye on the instagram account of a few other shops, even if they are too far away for you to get to, just to see what they carry.
If you know who actually orders stock, or who owns the place, they are more likely to be able to help you with things like that, as opposed to the casual worker or guy who is always chilling on the front counter. It might be one in the same, if it is just a small operation, but definitely get talking to them and casually ask about certain brands you would like to buy and that would be the first hint if they either don't want to or cannot get them in, or they actually want to help you.
The red flag for me would be if they say that brand is rubbish or something like that, which I have heard, or if they only talk up the brands that are currently in the shop (just so they can make a sale or clear out old stock) which again just shows how ignorant they can be of some things and make me want to shop elsewhere.
With regard to ordering, there are two main things to note, those being if the shop has an account with the distributor of the brands you are wanting, and cashflow of the business / if there are any conditions on the order or shipping costs which would make it not viable so they would not get that brand in, eg shipping cost of only a couple of boards means the cost goes up significantly for the shop, or they may not have enough spare cash to be able to put in an order, or they are not on good terms with the distributor.
Any or all of these factors could affect their stock purchases and it was a sad day when I would go back into a shop I hadn't been to in a while and see NOT a whole lot of new stock and a ton of almost vintage remnants still on the shelves, but if they are struggling, they might not be able to afford new stock, and many shops are closing all the time due to things like this.
I have probably said enough for now, but I would be interested to hear how you go.