Hia.  This is fantastic and beginning to look like I had envisaged..

Can I suggest a couple more alterations?

1) the particles now really clump at the bottom of the container with largely vacuum at the top.  could we maybe change the gravity effect into a relative vertical component vector.  By this I mean Ma =29 therefore relative to it's self it has a vertical force of 29/29 upwards and 29/29 downwards. Gas B has a upwards force of Ma/Mb and downwards force of Mb/Ma  and Gas C has a upwards force of Ma/Mc and downwards Mc/Ma.  This way lighter gasses will rise while Heavier gasses will fall. The space will be more uniformly filled without all the gas accumulating at the bottom..

The alternative is to incorporate some force of attraction towards the empty space that is higher for the smaller less dense molecules than it is for the heavier more dense molecules.. (this I think is quite a challenge..)

2) could you extend the temperature range to cover much lower temperatures.  This will slow the particles down and might help to lower the significance of the P-P interactions while not affecting the gravitational forces.