https://www.tsp.gov/PDF/formspubs/tspbk30.pdf
Just over halfway down there's a bullet on IFT's. This is the excerpt I was looking for..
"The second transaction you may want to
make is an interfund transfer (IFT). An IFT
is a transaction that allows you to redistribute
all or part of your existing TSP account
among the different TSP funds. For each
calendar month, your first two IFTs can redistribute
money in your account among any
or all of the TSP funds. After that, for the
remainder of the month, your IFTs can only
move money into the Government Securities
Investment (G) Fund (in which case, you will
increase the percentage of your account held
in the G Fund by reducing the percentage
held in one or more of the other TSP funds)."
So although it doesn't specifically say how many IFTs you can do in any given month, it does sound like you can do as many as you like. Hope this helps.