Here is an OCS RGB conversion table that I myself use:
OCS values (0-15) on the left, and normal RGB (0-255) values on the right.
0 = 0
1 = 17
2 = 34
3 = 51
4 = 68
5 = 85
6 = 102
7 = 119
8 = 136
9 = 153
10 = 170
11 = 187
12 = 204
13 = 221
14 = 238
15 = 255
Just make sure that the RGB values of your palette are set to those, and you can use any paint program to make OCS graphics.
