I've seen the 'Sorbopyrus' offered by a number of nurseries - OneGreenWorld, Mellingers, and others. My understanding, from seasoned orchardists is that they're mainly just a curiosity - not very productive, and the quality of the fruit is nothing to get excited about.

Karl

I guess it only allows one spot for a link, so the other one will go up here...:
NAFEX discussion of intergeneric Rosaceae hybrids

Pyrus, Malus, Cydonia, Aronia, Cotoneaster, Amelanchier, Mespilus have been crossed in various ways with varying results.

x Sorbocotoneaster pozdnjakovii Pojark.
http://www.biologie.uni-ulm.de/systax/dendrologie/xSorbcpozlv.htm

x Pyronia veitchii (Trabut) Guill. Cydonia oblongua Miller x Pyrus communis L.
http://www.biologie.uni-ulm.de/systax/dendrologie/xPyroveit.htm

Sorbaronia hybrida  (hybrid of moutain-ash and chokeberry, cultivated)
http://www.mta.ca/~rthompso/nativeflora/group5/Page57.html

Sorbaronia dippelii (Sorbus aria X Aronia melanocarpa)
http://www.arborealis.nl/pdb/output/items/1888.html

NC State's Mountain Horticultural Crops Research and Extension Center also lists some.
http://www.ces.ncsu.edu/fletcher/programs/nursery/accessions/accessions.html

Now, if someone would try bring the loquat (Eriobotrya japonica) into the mix, we might have something really interesting.

Karl