According to my latest spreadsheet as of 04/23/10 the number is 1,848. The top three on the list include:
1) NGF - 573 units (including Zupapa official production run)
2) Neotropolis - 281 units (authentic Kizuna sales not included)
3) Ray Young - 177 units (of which 165 are yet to be delivered to the Neo Store)
Some of the other notables are:
30) Wolf - 5 identical copies of Brikinger to store in
Wally Stevens' apartment
...
84) 8Man - 2 units, one each for his daughters to go alongside authentic Metal Slug collection
...
87) TonK - 2 units destroyed with Glock (I was present for said occurrence and participated in .75 unit destruction)
...
165) Kenny Perry Jr - 1 unit produced for the good of the community