Estimating close approach between all asteroids themselves
Thanks folks for helping.
I knew about SPK files but from Horizon's telnet inteface there is a limit of 200 bodies per request.
Making over 5000 request might be possible but not very productive.
I also looked at the  DE421 file from ftp://ssd.jpl.nasa.gov/pub/eph/planets/bsp/ but it looks like the corrections for the 8+1 planets
here is the output from BRIEF, a SPICE utility: https://naif.jpl.nasa.gov/naif/utilities.html
BRIEF -- Version 4.0.0, September 8, 2010 -- Toolkit Version N0066
Summary for: de421.bsp
Bodies: MERCURY BARYCENTER (1)  SATURN BARYCENTER (6)   MERCURY (199)
    VENUS BARYCENTER (2)    URANUS BARYCENTER (7)   VENUS (299)
    EARTH BARYCENTER (3)    NEPTUNE BARYCENTER (8)  MOON (301)
    MARS BARYCENTER (4)     PLUTO BARYCENTER (9)    EARTH (399)
    JUPITER BARYCENTER (5)  SUN (10)                MARS (499)
    Start of Interval (ET)              End of Interval (ET)
    -----------------------------       -----------------------------
    1899 JUL 29 00:00:00.000            2053 OCT 09 00:00:00.000

I can always do a statistical estimate, any close approach being false but the overall count being close to reality.
Too bad to drop the project, I was getting nices pictures from it. The coloring is done against eccentricity, red=0