RD series are still available. Local suppliers may be the issue but here in USA its widely
available. They work ok for 12V only designs.
Regarding IRF530, it can be used and does work at 30mhz but impedance matching
is harder due to the high input capacitance compared to the IRF510. I have driven a
IRF530 at 6M, nice 35w output at 28V but the input matching was 6M only. Like most
of the 100V mosfets they work much better with higher applied voltages on the drain.