First, note that for reparto, we want definition 2, "delivery," because the example provided ("No contamos con reparto gratuito") fits your context and because "en reparto" is a prepositional phrase. We know this because "en" is a preposition. So it wouldn't make sense for "reparto" to be a conjugated verb such as "I distribute."
Next, note that this phrase isn't a complete sentence. It's a fragment. Here is one possible interpretation:
[Hay un] envío [que está] en reparto para su entrega.
An equivalent to this very compact fragment might be:
Hay un envío que está en reparto, listo para su entrega."
Or something like that.
Post office speak is a bit special.