If you search digital counter board, amazon pops up with this 4 digit display (about 7.5cm long)that comes with some wires. It’s pretty inexpensive at less than $30 CAD. Something like that would work I think. Not too sure how I’d get it to work I’d have to order it and play around with it.
https://www.amazon.ca/Red-LED-4-Digital-Digital-Counter/dp/B00CB9ZXBO
Why don't you just Buy one?
up down digital counter search.
Maybe a chalk board would be better? You can keep up with it through out the season
you could possibly piece something together with three of these and six of these. You would also need a power supply. I think 4 AA batteries would suffice, but I am not sure how long they would last. You could have a master on/off switch for it, as the counter I listed advertise that they retain memory if a power failure occurs.
I'll have to think this one through some more.