For my marketplace, I was friends with someone who could make it look like not a ghost town for the supply (an established game store with lots of trading cards in stock). Then, we struggled to get more sellers. Then, we found channels to get selllers, which were basically software systems we could build integrations with. The integrations de-risked the proposition for sellers enough to get more traction. Eventually, if you have growing volume, the supplyside just starts coming on its own mostly, and you focus on retaining sellers and growing buyers.

For your marketplace, you could bring the supply-side by Fedexing stuff when you don't have a carrier. You'll have to lose money on the initial shipment, until you can route the jobs to the supplyside. This assumes you think the typical use case for this isn't smuggling.

The amount of jobs may be low enough at first that you can be like "You said Cairo to London, that will be $N." Then, if you can fill the job manually by finding someone somehow, then you add them to the platform and they do the job. If not, you send a prepaid mailing package with a Fedex label to the recipient and they ship it easily, and you subsidize it so it seems like a great deal to them.

Limiting geography seems like a good approach too.