I have had good results searching for tailwheels for gliders at wheel chair parts sites. Google "wheelchair front caster". My favorite supplier "MobilityDirect" appears to have gone away, unfortunately. http://www.wheelchairparts.net may be a good place to start.

That's the place I got a new tail-wheel tire for my Libelle, which was white and an odd size. They seemed to have a good selection.

Uli
'AS'