Where can I get the actual data to calculate this?
If you are a programmer, you could use the SPICE library: https://naif.jpl.nasa.gov/naif/toolkit.html and the data files available here: https://naif.jpl.nasa.gov/pub/naif/generic_kernels/spk/planets/ or you could use https://wgc.jpl.nasa.gov:8443/webgeocalc/#StateVector or HORIZONS: https://ssd.jpl.nasa.gov/horizons.cgi
The masses are listed here: https://naif.jpl.nasa.gov/pub/naif/generic_kernels/pck/ file "gm_de431.tpc".
For example, the state of Pluto (here I'm using Pluto system: Pluto + satellites) on 2021-01-27 00:00 UTC in the mean ecliptic and equinox of J2000 reference frame is:
r = (2.11488 · 1012, -4.65878 · 1012, -1.13045 · 1011) m
v = (5088.6; 1090.04; -1584.49) m/s
GM = 977 · 109 m3/s2. If we use G = 6.6743 · 10-11 m3 kg-1 s-2 (https://physics.nist.gov/cgi-bin/cuu/Value?bg), M= 1.4638239 · 1022 kg.
L = r x Mv = (1.09861 · 1038, 4.06324 · 1037, 3.80771 · 1038) kgm2/s, the magnitude is 3.9838 · 1038 kgm2/s.
If we do the calculations for 20 years ago (2001-01-27 00:00 UTC) we get:
L = (1.09685 · 1038, 4.04601 · 1037, 3.78485 · 1038) kgm2/s, the magnitude is 3.9613 · 1038 kgm2/s.
For Mars, 1970-08-25 00:00 UTC (the notation 123e+011 means 123 · 1011):
r = (-1.9051451e+011; 1.58990113e+011; 8.02428218e+009) m
v = (-14604.5348; -16539.1841; 13.5952337) m/s
L = (8.65493375e+037; -7.35385224e+037; 3.51194063e+039) kgm2/s
||L|| = 3.51377655e+039 kgm2/s.
For today (Jan 28) I get:
r = (4.11669129e+010; 2.27295989e+011; 3.75334592e+009) m
v = (-22924.868; 6375.0766; 695.965252) m/s
L = (8.61551162e+037; -7.35994071e+037; 3.51209564e+039) kgm2/s
||L|| = 3.51392307e+039 kgm2/s.
WARNING! Do not to assume that all the digits are significant. I wrote the numbers with an unrealistic accuracy just to verify the calculations.
It could be interesting to see the variation of L against the time.
The following graph shows the value of (L - Lmin) / Lmin, where Lmin is the smallest calculated angular momentum and L is the instantaneous angular momentum.
The calculations are done with the SPICE library and the DE430, jup310 and mar097 ephemerides. The independent variable is the time wrt the orbital period of each planet. The starting epoch is 2021-01-28 00:00 UTC.
The graph is as expected. Mercury, well inside the Sun gravity well, is only slightly perturbed by the other bodies.
The Earth is heavily perturbed by the Moon and also Jupiter is significantly perturbed by its moons.