Get IrScrutiniser.  On the Generate tab, select RCA-38 as the IR protocol.  Enter 0 into the D field and the command bits into the F field, then click Generate.

For example, Key_HDMI1 (enter 0x48) is
0000 006B 0000 001A 008E 008E 0012 0024 0012 0024 0012 0024 0012 0024 0012 0024 0012 0047 0012 0024 0012 0024 0012 0047 0012 0024 0012 0024 0012 0024 0012 0047 0012 0047 0012 0047 0012 0047 0012 0047 0012 0024 0012 0047 0012 0047 0012 0024 0012 0047 0012 0047 0012 0047 0012 011D

The timing information from TCL above differs slightly from normal RCA.  If the Pronto Hex doesn't work reliably, try editing IrpProtocols.ini and change
irp={38.7k,460,msb}<1,-2|1,-4>(8,-8,D:4,F:8,~D:4,~F:8,1,-16)+[D:0..15,F:0..255]
to
irp={38.7k,500,msb}<1,-2|1,-4>(8,-8,D:4,F:8,~D:4,~F:8,1,-16)+[D:0..15,F:0..255]