You mean the metal bit not the cheap plastic one...
Any leather accessories shop would have them.
Unfortunately, all the sites I know are UK based so no good for you.

 

I am missing one of the combinations of pieces in the picture.

 

The plastic male buckle, the bottom strap, and the metal buckle. Thanks

 

They are called roller buckle or pin/roller buckle

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You would have to make it yourself (or get a shoemaker to do it for you)
They are fairly easy to make, the plastic lock will be available on outdoors stores, they come on different sizes.
All of it you can also get from ebay.
It looks like the bits are held together by the metal crush pin between your fingers. so I would say is a 3/10 difficulty level

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Forgot to mention.

The strap you just need a leather belt and cut it to size. I'm sure you can get one for a couple bucks.

 

Thanks, I am exploring this option right now.

 

Try any outdoor store for the plastic buckle and leather goods or sewing store for the metal and leather.

Here we have
Buckles and accessories | MEC
and
Roller Buckles — Tandy Leather Canada

 

Check Tandy Leather. Use to have a brick and morter stores.
Will prob have to buy the pieces and sew it yourself.

 

Basically what you will need are 2 leather belts cut to the length you need the straps. Then attached the plastic buckle on the other end.
This way the metal buckle is already fitted and you only worry about the plastic bit which should be easy to fit.
Even better if you have a shoe repair shop and ask them to fit the plastic buckle.

 

Hobby lobby should have everything you need as well.


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