A2000? 10Mb/s - YES, 100Mb - NO
10Mb new would be X-Surf from many supplies new like
Software Hut. They arent cheap, run about $120USD but also include IDE and clockport interfaces.
10Mb used there are alot of second hand options like the Commodore A2065, watch ebay.
If you had a newer Amiga than a A2000, then you COULD get a off the shelf 10/100Mb PCI ethernet card. If you had a A1200, A3000 or A4000 you could buy a Mediator PCI exansion and then buy one of the supported 10/100 cards off the shelf.