I'll try to help.
Go here:
https://apps.kubotausa.com/illustrated-parts/
Agree to the legal stuff, then type in B2100.
There are 4 versions of the B2100 - depending on 2WD/4WD/ geared or HST.
Pick a model, and click "OPEN" to open the parts illustrations.
Then expand the "HOOD/BONNET/ROPS" option by clicking the "+" next to it.
Then select the "STEP" option. Seems part 090 is the common part for the floor mat in the diagrams.
The floor mats for some models are different depending on Serial # - other models are the same throughout the model's life.
The 2 part #'s I found were:
6C040-51361
6C040-51364 - this one seems to be the more common and later version for later SN's.
Don't know if these links will work - but looks like Messick's and Coleman's have the more common one in stock for ~$90.
http://www.messicks.com/part/6c040-51364/mat-step
https://www.colemanequip.com/search/6C040-51364/
Good Luck!
