Remember that you can produce 5 cavs from a single province per day.
I believe upgrading your Workshop and Factory increase production speed for all units besides infantry:
There is also a benefit for partially built factories.
For cavalry and armored cars specifically:
Level 1 Workshop: 2 Days
Level 2 Workshop: 1 Day
Level 1 Factory: 1 Day
Level 1.25 Factory: 19 Hours 12 Minutes
Level 1.5 Factory: ?
Level 1.75 Factory: ?
Level 2 Factory: 12 Hours
Level 2.25 Factory: ?
Level 2.5 Factory: ?
Level 2.75 Factory: 8 Hours 40 Minutes
Level 3 Factory: 8 Hours
Level 3.25 Factory: 7 Hours 20 Minutes
Level 3.5 Factory: ?
Level 3.75 Factory: ?
Level 4 Factory: 6 hours
There are 16 total health on a factory. Each quarter level AKA 12 hours of building speeds up unit production.
So at best each province can produce 4 cavalry per day. Someone else feel free to fill in the gaps. That all I can remember off the top of my head and checking my active game.