DCF77 antenna preamplifier from available components
Here is a JFET preamp for a WWVB receiver (60 KHz instead of 77.5 KHz):

It comes from this youtube video:
https://www.youtube.com/watch?v=qeYQvsAtdf0
and this tweet:
https://twitter.com/codedweller/status/638824875340132352
I think you could use pretty much any JFET device in place of the NTE457 that has similar specs. You might have to use a SMD package -- e.g. a J309 in a SOT23 package.
The BC550 is just a jellybean NPN transistor. It shares the same datasheet with the BC546, BC547, BC548 and BC549 all of which would probably work.
https://www.onsemi.com/pdf/datasheet/bc550-d.pdf
Two other jellybean BJT designs for WWVB to consider:

Hans Summers: http://www.hanssummers.com/images/stories/radio/report.htm
One by Russell Kincaid published in Nuts and Volts, May 2006: