At 50MHz, you should find that metal-oxide resistors will work fine.
You're just making a power-wasting pad, not a precision attenuator.
(Carbon comps wouldn't be appropriate for precision work, either...)
The low-value metal-oxides I've tested on RF component analyzers have
all been fine for non-precision applications out to 150MHz. Try, for
example, Vishay FP69 series 2W parts or TT/IRC GS-3 series.

A couple years ago, I went through my stock of carbon composition
resistors and found more than half of them to be out of tolerance at
DC. They don't age well at all, even while not dissipating power.

1/8-W SMT resistors are so cheap that you could just use
series-parallel combinations of them to get what you need, too. For
more serious power dissipation, Caddock (and some others) have power
film resistors in TO-220-like packages which are low enough inductance
to be quite useful up into VHF and maybe above.

Cheers,
Tom