Dark fiber is rarely available through residential ISPs. Major sellers include:

Firms like Uniti and Cogent often sell to hyperscalers (Amazon, Google, Microsoft) or large enterprises.

For an IRU, you might pay an initial sum (e.g., $30,000 for two strands on a specific route) to secure the rights.

Negotiate specific "Mean Time to Repair" (MTTR) for physical fiber cuts.