For what you want, I'd be

For what you want, I'd be tempted to take the motor out of a 9G Servo and use the gearing there, They're cheap enough it wouldn't cost much....cheaper than you're likely to find a separate gearbox for.

If you have access to the

If you have access to the Model Railroader archive,  Lance Mindheim did an article in the April 2013 on using 2 locomotive trucks to open and close the gates.   Joe

I seem to remember someone

I seem to remember someone building a gate mechanism out of Lego parts. They have both gears and shafts.

Try a locomotive gear box

A steam locomotive gear box from NorthWest Short Line would work

A 28:1 gear box  would only require 7 turns to move the gate 90 degrees

Howard Garner

 second hand ultra light

second hand ultra light spinning reel. Remove the spool and the bail , the outside shaft should rotate , you can use square stock for the drive in place of the handle .  The hard part is mounting. Otherwise you can disassemble ,use the gears /shafts and make your own box out of PCB/brass.

bevel gear box

Else you can buy 90 bevel boxes on ebay ...they're expensive ~ $40 +

Ken - I hate to ask, but why

a gearbox?  even a push-pull rod would allow 90 degrees, with the right linkages.  If you really want to rotate a knob, it still can be done with a shaft and appropriate linkage.

Just curious.  If the answer is "I want to do it this way", that's fine.

Blair

This guy used legos

And here is his blog:

https://www.thomasklimoski.com/how-to

Awesome layout and his operation gate and door are pretty crafty. 

I am pretty sure this is the guy that @on30fan is referring to as well. 

How wedded are you to 1/8" drive size??

If you are prepared to do some fudging on the size of the drive, then perhaps here's another 2 options from Tamiya:

1. https://www.tamiyausa.com/shop/educational-construction/shaft-drive-unit/none/  this gives you a 3mm hex-shaft drive
2. Cannibalise something like this from their Mini 4WD range

You will probably need 2 kits - one kit drives the each of the 2 gates, one of the 2 drives from the second kit transfers the drive out to the fascia. 

90 degree drive

John that is perfect for what I want to do  !  I'm ordering one now ! Thanks for the link !!  --------- Ken 

Yes, thank you. That is the

Yes, thank you. That is the layout I was thinking of, 

Direction?

That 4 wheel drive unit will have both the parallel shafts turning the same way. For a pair of gates, I'd expect them to go in opposite directions.

I was going to suggest that

I was going to suggest that in many cases you can build very complicated gear boxes from Lego gears.  And I believe that lego has a software you can use to design anything in 3D (lego wise) and I believe they sell the lego parts individually.

-Doug M

Re: Direction

Hi John,

for the Tamiya unit  Tamiya 70225 Shaft Drive Unit / Tamiya USA  from the instructions in the link

That's why I thought that this option might be a possible solution to the problem posed in the OP.