Having trouble for a low pass trap filter parts selection

I am working on a low pass trap RF filter. The purpose of it is to allow all the low frequency signal to pass through the filter but prevent all the high frequencies coming from the RF device. The problem is the cuttoff frequency is at 3KHz but the RF frequencies goes up to 300 MHz. So finding the right parts for the design is a dilemma as all the inductors used have a very low SRF, and if I want to use inductors with large SRF (i.e air core) I will find only extremely small inductance for sale as opposed to a very high inductance needed to design a Low pass filter at 3 KHz

You might be able to use a large magnetic core inductor in conjunction with a smaller air core inductor to get the response you need.
Or use an active filter for the low frequency filtering.