I did increase my TSO trigger pull using a Tanfoglio sear spring. It increases it by about .25 lb. I also increased the main spring to 26lb that increased it about .25 lb. In conjunction with the heavier main spring I installed a heavier firing pin spring from wolff.
Chronicled here:
http://www.czfirearms.us/index.php?topic=86250.msg645137#msg645137I haven't measured the trigger pull now that the TSO is fully broke in (~2000 rds). I should just to see how it has changed through use.
Those that have a trigger pull that is ultra light, I wonder if your sear/hammer hooks have been rounded off? You need to inspect them to ensure they are still sharp. You also need to inspect the trigger over travel screw adjustment. If it isn't adjusted properly, you can damage the sear on the hammer hooks. Even though the TS/TSO trigger pull is light, there still is an actuation point before break. You should feel it, if you don't then I would assume that the hammer hooks/sear are damaged.
Procedure here:
http://www.czfirearms.us/index.php?topic=47884.msg283196#msg283196I'm not aware of a heavier/lighter trigger return spring for the TS line. They are not the same as the 75 series. The sear springs are the same and I'm unaware of different weight options for those.
Cheers,
Toby