Estimated values for CH4 I from:
Brown, G.N., and W.T. Ziegler 1980.  Vapor pressure and heats of vaporization and sublimation of liquids and solids of interest in cryogenics below 1-atm pressure.  Adv. Cryo. Eng. 25, 662-670.
T(K)     P(bar)
90.60   1.16e-01
88.60   8.69e-02
86.60   6.40e-02
84.60   4.65e-02
82.60   3.32e-02
80.60   2.33e-02
78.60   1.61e-02
76.60   1.09e-02
74.60   7.20e-03
72.60   4.66e-03
70.60   2.94e-03
68.60   1.81e-03
66.60   1.08e-03
64.60   6.22e-04
62.60   3.46e-04
60.60   1.86e-04
58.60   9.53e-05
56.60   4.67e-05
54.60   2.17e-05
52.60   9.50e-06
50.60   3.90e-06
48.60   1.49e-06
46.60   5.22e-07
44.60   1.67e-07
42.60   4.80e-08
40.60   1.22e-08
38.60   2.70e-09
36.60   5.07e-10
34.60   7.88e-11
32.60   9.78e-12
30.60   9.28e-13
28.60   6.38e-14
26.60   2.96e-15
24.60   8.44e-17
22.60   1.29e-18
