You will have several local bolt/fastener shops that sell little else, like bearing shops, the trade is brisk enough they don't advertise or try to find customers, customers find them. Its an industrial supply so wherever you have some light industrial estates...
I find they're not often open outside of normal hours and they're difficult to order and ship from. Maybe I've been spoilt by mouser/digikey search tools and variety
The industrial suppliers don't need your business, they do fine without the hassle of tiny online orders (if you do find such a shop selling online the prices are massively inflated to cover the expenses). Its nice most of them open on weekends for people who cant make it during business hours. You want a very specific xyz fastener, then suck it up and go through the channels available. Walk up to the counter and have a chat with them, you might be surprised with how knowledgeable and helpful they are providing value add. Electronic parts is one of the few industries that has simplified the distribution chain, almost everything else is still:
contract manufacturer -> brand "manufacturer" -> importer/wholesaler -> retailer -> customer
If its such a great market, open your own fastener retailer with wide range, long opening hours, and online sales.[sa]Thats sure to be a profitable enterprise[/sa]. If you like digikey then they already have a range of fasteners and mechanical parts through their shop (1st party, not just through the partners/platform).