You can easily build a Rohloff wheel or have it built by several online shops in Germany.

But to mount a Rohloff on a Birdy as done on a factory built Birdy Rohloff, R&M and Pacific Cycles use some specific parts that can only be ordered from them.

About the easy wheels, the link you gave says: estimated delivery to Belgium Aug 1st. Its one month but my experience is that the estimation is not reliable, the actual delivery time is unpredictable because orders of several customers are grouped for shipment and then the shipment is awaiting for an affordable shipment opportunity.

The problem of long delivery of items coming from China (not only Aliexpress) is a consequence of covid and the huge increase of shipment costs.