I'm following this paper to calculate geocentric coordinates. The authors have provided the initial mean longitude values for the planets (provided in attached table) for 01.01.2000 @ 00.00 UT but I'd like Uranus, Neptune, Pluto and some asteroids also. Is there anywhere this information is freely available or did they calculate it? Many thanks.
Take a look at this link. It included Program Codes Listing also (Appendix C). But if you only want the initial mean longitude and the angular veclocity... the appendix C.1 does have them listed at the beginning... in it, the values are L0 and n for each planet... (The n in the listing is in arcsecond, you have to divide it bye 3600 to get your desired degree value.)