You can go and buy an expensive VST that has the brass sound, but my guess is that will be missing something too.
I suggest the following:
1. Record the best brass sound you have
2. Copy the track
3. Move the start of the orginal track back a few milliseconds
4. Move the start of the copied track up a few milliseconds
5. Pitch the original track down about 6 cents
6. Pitch the copied track up about 6 cents
7. Pan the original track left a little bit
8. Pan the copied track right a little bit
9. Send both tracks to a aux/group track
10. Compress the aux/group track just a touch
11. EQ the aux/group track to taste
12. Send the aux/group track to an FX track
13. Put a delay on the FX track
14. Put a reverb under the delay on the FX track
15. Create a new track and choose a thick bass for your patch
16. Copy the data from the orginal track onto the bass track
17. Play with volume of both the aux/group track and bass track to get a good balance
Presto, now you have a brass sound that is thick, airy and with a nice low end.
Of course the above is just one suggestion. It might not sound what you want, but this is just a way to open your eyes a little bit as to what you can do to sound to manipulate it into something you want. It not as easy as just picking a sound sometimes. You have to identify the sound you want in your head and understand what steps need to be taken in order to get that sound. Most the time it is the mixing that make a sound, sound great, not the orginal patch. Hope this helps a little. Good Luck.
-DG