When I went for my tickets, there was grand final merchandise on sale in the clubhouse with the tickets, all manned very well by polite volunteers.
If you've gone and there wasnt any merchandise, my guess would be that the initial batches have sold out, which means the club is probably doing very nicely from it. I'm sure there'll be more stock coming as the week passes and doubtless the club shop will be open on Sunday morning as you arrive for the bus.
The clubs aims towards the end of a regular season should be to run its stock down in readiness for new lines in a new season, it surely cant afford to throw old stock away. Since winning the title, a new polo, flat cap, T-Shirt, pin badge and mug range has been developed and put in stock and I'm sure there have been regular new products throughout the season as well. (Introduction of the Est 1921 range for example).
The think white & blue striped shirts have been on sale for months, the stock left is the remnants of this design.
Where have you been all year? Just noticed we've made a final?