The only dictionary I found torbie in was Wiktionary ("A diminutive form for tortoiseshell tabby cat"), and I didn't find it in a few corpora and newspaper indexes. However, it is used by quite a lot of cat-related websites and books, so I think it qualifies as a rare word.
The spelling torby is used occasionally, but not enough to persuade me to include it. So this means the plural torbies will not be acceptable, except in puzzles that allow all plurals.
