first of all, are you talking about actual RFID or NFC ?
secondly, I dont think youre going to be able to find one.
thirdly, theres no reason you cant use one with the reader on the back of the tablet.
And lastly, in my personal opinion Unless the app you wish to develop is specifically for tablets, it would be much cheaper to go out and get an old, maybe second hand phone or even a nexus 4 because of how cheap they are in comparison to a tablet
Current Phone: Samsung Galaxy S4 GT-I9505G GPE ROM Rooted Phillz Touch 6.00.2
Current Tablet: Sony Xperia Tablet Z SGP311
Past phones in order: iPh4, LG KM900 Arena
, Nokia 6210 Navigator
,2x Unknown Nokia, Motorola Razr V3
, The Simpsons Phone.
A lot is known about me in this place, "Internet" And some day, I hope to reside here along with all the data.