you can get a rough estimate if you make a guess of the power going to
that tail rotor. there are varying numbers depending on helicopter but
you can assume 15% of the total engine power delivered goes to the tail
rotor. then you can use the equations below to estimate the number:

assume 400 hp helicopter engine, operating at max power
power to tail is 15% of 400 or 60 hp
power loading (PL) on a 6 foot disk is about 2.1 [hp/ft^2]
thrust loading (TL) is calculated using the following:
TL=8.6859 * (TL^-.3107) [lb/hp]
in this case, TL=6.89 pounds per horsepower
so thrust is approximately 400 pounds