does anyone know of (or have) a working physical model of a bowed string for
pd?
For musically effective externals/patches you should look at Stefania Serafin's site: http://ccrma.stanford.edu/~serafin/ She's got her PhD in Stanford with J. O. Smith and now works in Denmark (http://www.imi.aau.dk/~sts/)
We in Verona (http://www.di.univr.it/dol/main?ent=arearic&id=3&lang=en) have developed some physical models of interaction (impact and friction) between resonators. The software package was originally developed within the European research project Sounding Object www.soundobject.org and consisted of externals and patches for pd. On the aforementioned site you'll find the old package with modal resonators only. At present the package includes 2 kind of resonators: a modal one and a waveguide one, the latter simulating a simple string. I'm currently rewriting the externals for flext. Note that our package is not intended for musical purposes, indeed the control parameters are not musically functional (e.g. the "bow" has infinite length and one can only control the force pulling it and that bearing it down on the string). Nevertheless, if you're interested, we can give you a copy of the source code with makefiles for linux, mac os x and windows.
Stefano