Fascinating. I've never seen it before. There have been 9 born in England between 1850 and 1930, all in the North of England. (Sorry, I don't have access to Scottish records) I had a poke around and came up with the page from the lingerie lady pointing me to Orkney, and then umpteen Orcadian genealogies with Tomimas in. No useful info really. The Tomine / Tomina / Tomima via Jemima theory seems plausible to me, but you'd probably need doctoral funding to prove it!
Nice name though, especially with all that family history attached.