Are the gold skins still earnable?

No im afraid not as these had a timeframe to complete by before gears 5 came out.

The Gold Skins, or as they are called in game "Gilded," were only obtainable through the completion of the "Road to Gears 5" challenge achievements that were available from about mid-August to September 2nd I believe on Gears of War 4. With the exceptions
of eSports Kait and Gilded RAAM both being special events prior to the other Road to Gears 5 challenges.

They are no longer obtainable. This is due to their nature of being a promotional sort of event. They will most likely be obtainable again in the future when Gears 5 starts doing challenge achievement events similar to how Gears 4 did a
few times every ranked "season." I would, however, take that with a grain of salt.

I got a majority of the skins with the exception of Gilded RAAM, Gilded JD, and eSports Kait. Part of the reason being timeframe and the difficulty of the challenges.

To reiterate, you can no longer get these skins.

I was under the impression the only way of obtaining the gold skins was as a pre order bonus or as a pre requisite from gears 4

unfortunately not, i have just logged in and checked, i managed to get the gilded weapons but nothing else

Sadly it does not appear to be the case at the moment, but you never know, they may include it as DLC in the future.