As a Logistics leader or Distribution leader, who do you typically get your 6 week outbound rolling forecast from? S&OP? Demand planning? Sales? or other?

As an erstwhile industry practitioner and then a consultant with some experience, I find distribution leaders focussing on sales plan/orders more often than not.

This isn't entirely misaligned to where one needs to be. Ideally for the near term, 6-week horizon you would want distribution to focus on most recent/plan cycle S&OP/ IBP numbers and service the sales needs on weekly/ daily basis based on firm orders. This needs to be coupled with sense, measure and adjust for agility, flexibility and deviation to plan. Appraise planning team on plan accuracy as you would appraise distribution on fulfillment/flexibility and resilience.

Focus on the overall IBP plan for tactical shipping capacity/space/labour needs with 3PLs/logistics partners.

As logistics execution is at the very end of the planning process, it depends on the business and planning strategy one is employing.
If it is straight MTS (make to stock, or serviced from stock), then information comes from the running sales order book and consensus demand (S&OP), in the end S&OE process.
If it is MTO (make-to-order), or ATO (assemble to order), then information comes from the confirmed production orders linked to customer orders.
These sub-functions can supply your logistics execution plans for the coming, rolling 6 weeks for sure.

Typical 6-wk outbound rolling forecast comes from the S&OP alignment. S&OP accounts for demand planning and production/supply commits.

The six-week rolling forecast is initially developed by the Data Analytics team based on Store/SKU forecasts, adjusted for seasonality. This is aggregated at the corporate level for Finance to make any adjustments to the estimates to meet the financial plan, typically referred to as a stretch forecast. In an S&OP meeting, these numbers are discussed by all the stakeholders, where marketing may have a top-level target, and sales may bring in an account-level target. These numbers are presented to the P&L owner (GM or above) for deciding what the actual targets should be. Then, the number is sent to the DCs (based on the supply chain network design), and inbound-outbound shipping targets are finalized. If manufacturing is in-house, the numbers are also sent to them.