Best FIX library for .Net (C#) is QuickFIX .You can use it for getting your requirements. If you find some bugs ,then you can post it on QuickFIX forum ,they people solve it without any cost.i am using it for more than 2 years.
VersaFix is also second alternative for you .You can also use it with .Net plateform.It has almost same feature as QuickFIX.You can get source code an others from VersaFIX link.
If you are looking for third party dll(library) ,it depends upon your requirement and subscription types and times.But Onixs has a very good api for your requirement and it is bug free with very good support.
Other third party API for FIX implementation QXFIX from ModulusFE .It is very new FIX engine having all features like support for all updated versions of FIX and FAST.
FIX Antenna is Other alternative for you ,supports all FIX versions and FAST 1.1 without any bug :-) ,good with .Net for fast data transfer on network.