Most British vintage radios, test gear and other vintage electronic equipment used a range of BA nuts, bolts and screws, and for knobs, set makers generally used BA grub screws. Also, BA thread rods were used for assembling banked multi-wafer switches and so forth. For a little while now I've used a small firm appropriately called 'B.A. Bolts' though they also carry a wide range of other imperial threaded hardware and metric too. As well as nuts, bolts, grub screws (both slotted and hex headed), and threaded rod, they also stock a range of rivets in aluminium, steel, copper and brass, and taps & dies.
They also stock BSW,BSF, UNC, UNF.
Basically, they cater mainly for the model engineering fraternity.
Occasionally vintage radio restorers who have to remove valve-holders riveted to the chassis ponder on whether to use rivets (which may be difficult to 'set' even if suitable ones can be found), or to take the easier route of nuts and screws. 'BA Bolts' carry a range of round headed unslotted bolts which mimic the appearance of rivets.
They claim to carry most items in stock and orders received before 3.00PM are processed the same day. Postage fixed at £2.50 for UK orders, and their minimum order value is only £1.00 plus postage. Their turnover appears to be below the VAT threshold so no VAT is charged on orders.
As well as PayPal, they accept personal cheques / postal orders / Bank Transfers, and will post worldwide.
Worth a look at their website, which is nicely set out and easy to navigate:
https://www.ba-bolts.co.uk/index.html
I've no connection with them other than as a satisfied customer. I'm prompted to mention this little firm because I placed a trivial order with them last week, which was only for a 6" length of 4BA threaded rod. £1.80 - it arrived next day.
Hope that might be of interest and use.