turbo wastegate question

[nismo tuned s14]

i have the greddy (mitsubishi) TD06SH-20G turbo with the infamous small wastegate. i have the greddy turbo kit for the KA. i cut out the restrictor in the turbo inlet pipe and i also have an after market downpipe which aids in the boost creep. the stock kit is only supposed to boost around 8 PSI, but now it holds about 14 PSI every time it's at wide open throttle (without the boost controller hooked up). i recently bought a boost controller, and i cant control the boost. the boost controller was installed and set up properly, but the boost will go way higher than what it's set at every time. it caused my ECU to throw a knock sensor code that i cant get rid of.

my question:

i've looked around at different internal wastegates, but i dont know which one will fit on my turbo. which one do i need? can i just replace the spring?

i searched the web without any luck. i dont want to go with an external. i need a wastegate that bolts up and will take around 350hp daily. also if anyone knows how to get rid of that damn knock sensor code that'd be helpful. (i'll probably just start a new thread later)