What are good options when a server delivery gets pushed way out?

First check whether this actually needs to be a new physical server. If you already have suitable virtualization capacity, a domain controller VM may be the quickest route, subject to licensing, capacity, network access, and the client's requirements. If the need is mostly redundancy, a properly connected VM at an existing site could also work.

For a smaller setup, a temporary VM on an existing host or even suitable spare desktop hardware can bridge the gap. Treat that as a stopgap, not an automatic production design: make sure backups, power protection, security, and a clear replacement plan are covered.

Refurbished or used enterprise gear can be much faster to source, and another vendor or an in-stock configuration may have a shorter lead time. Ask suppliers to confirm the unit is physically available, its exact configuration, warranty and support terms, and the delivery estimate in writing. A listed product is not necessarily sitting on a shelf.

If the workload can be hosted off-site, a temporary cloud VM is another route. Compare ongoing cost, connectivity, licensing, security requirements, and how you would migrate or retire it once the physical server arrives. That can be a practical bridge, but it is not automatically cheaper or simpler.

Get quotes from more than one reseller and ask specifically for in-stock or ready-to-ship systems, not just a new build with a hopeful date. If this is critical infrastructure, plan around the confirmed lead time and avoid promising a delivery date based on an estimate.