I think you will struggle to get tickets for this game for two reasons. Firstly Brentford's stadium is the second smallest in Premier League with a capacity of 17,250 and we will only receive an allocation of 10% of that capacity or around 1,700 seats and secondly it is a London game so it will be very popular because it is very convenient to get to. For the other London games, all in much bigger stadiums, we receive 3,000 tickets and tickets for these games always sell out. We could probably sell twice as many tickets for the Brentford game as Brentford will give us.
Tickets for away games are sold in bands depending on how many loyalty points each fan has, with loyalty points being awarded for attending home and away games, buying merchandise from the club shop etc etc. Because we only receive a small number of tickets for the Brentford game, the number of loyalty points required to buy a ticket will be very high.
It is possible that someone with sufficient loyalty points may buy a ticket and then find they can't go at the last minute and put it up for sale on this site but even that is unlikely, especially if you want 2 (or more) tickets together.
England