My guess would be that John Tulloch is no longer in business.John Tulloch down in Selkirk used to be based in the Shetlands but moved to the borders and specialized in Shetland knitwear. The web site is now defunct but they may still be in business and supply private labeled knitwear to shops in Edinburgh. I doubt that you would want to go to the trouble of sleuthing this, just a thought.
The Scots knitwear industry has changed rapidly since the turn of the century. Old names fold, newer small operations spring up. The Shetland Knitwear Trades Association has removed its member links www.skta.co.uk
Last year I picked up a bunch of shetland crew-necks very cheap from Clothing Discount Co., an end-of-range shop in London.
They had a wide range of shetland knitwear in various styles. The labels were John Tulloch, Glen Tor and McAdam.
The shop closed last October, a victim of re-development.