It's often hard to get something which will pass for period towels - ie before the era of the fluffy towel. These modern towels I think can look the part - they are a pure cotton woven fabric, which looks like linen, with an edge stripe and also a tasselled fringe.  This could be cut off and the ends re-hemmed (by me for an extra charge, if you want.)  They are 56 x 81 cm at present.