here is a partial list (
link will open a pdf file) . . . it's supposedly official, but we know it is partial because they have no listing for the number 8, which belonged to Hall of Famer Vic Hanson. Don't know how they could miss that one. "8 Hanson" would be a cool customized jersey, IMO.
Personally, I would go with 19 which is one of the numbers worn by the legendary
Wilmeth Sidat Singh (he also wore #3, but there are a ton of #3 jerseys around). However, if you get "03" then you honor the only NCAA title. following that line of thought, an 18 or 26 would be cool because nobody else would have them and you could honor the school's first two national titles, awarded for the the 1918 and 1926 seasons.