External toolbox cover for 1979 BA-1100 model

Hi everyone!

We recently bought a 10 foot tent trailer, the model is BA-1100, and the external access lockable box in one of the front panels had a broken door.  It was being held on with an occy strap, but that failed along a particularly long stretch of hwy, and now there's a big hole where you can see all the tools.  So yeah, we need to replace it, but I have no idea where to start looking for parts.  If anyone on here has any ideas or even has one I could purchase I'd love to hear about it.  We live in Banff, Canada, but its not a large or heavy part and I'd be happy to pay any postage.

Thanks!!

Here are a couple of pictures, so you all know what I'm talking about....

https://i.servimg.com/u/f39/18/98/82/68/win_2012.jpg

https://i.servimg.com/u/f39/18/98/82/68/win_2013.jpg