The Fb Milwaukee cards are indeed scarce, close to California League territory, as are some of the other Fb cards. If you are after a team, player, or pose that is only known as an Fb you could spend a lifetime waiting for one to surface. When I moved to Iowa 8 years ago I thought it might be interesting to obtain an example team card of all the Western Association teams from 1888 and 1889 and quickly realized that was a tough task. Most of the Western Association cards from 1888 are Fb and rarely surface. A single example from Milwaukee, St. Paul, and other teams may not surface for years. Fantastic pick-up on the Schenkel Jay! Finding an example from the Chicago Maroons, a recognized tough team, was actually much easier than the other teams (a couple Chicago & Des Moines players seem more available than others). Even outside of Western Association there are a lot of very tough Fb cards, think Anson in Uniform, McGreachery (or the other half of the Deacon White poses), 3rd Harry Wright pose, etc.
Regarding Fb script, they do exist. I suspect these came about when some of the Fb poses were created later in the year, after the negatives had been modified for cabinet cards. Here are two examples.