you can indeed sometimes find the N950 on eBay, for $$$$$
If you search you will find enough sources to learn developing for sure.

http://item.mobileweb.ebay.com/viewi...d=261230401221

do you plan to develop applications, or mods to the system kernel, drivers, modules ? would love one more looking at
NAT support for iptables
injection drivers for WLAN

sources from Nokia is available here
http://maemo.cloud-7.de/HARM/N9/1.3/

Looking forward to see your work