I like Pawel B's comment about layering Kanban over your Scrum. I do think Scrum can accommodate what you are looking for if you really want to keep to Scrum...
- Stories have external dependencies - Do you have the User Story correct? (Might you do well splitting it into 2?) Can you complete something that provides value to your customer (market) without the feedback? Maybe the User story captures the tasks to produce the first version and if the feedback comes in, you can take off the other User Story in the Backlog "Update with Market Feedback"
- Stories have external dependencies - Scrum might be pointing out that what is missing is a different customer/information management technique. If getting feedback is of critical importance, "waiting for a callback" doesn't seem up to the task to accomplish this. What about holding a "launch party" or some other marketing event that drums up interest and ensures you can get the feedback you need?
- Strict deadline - This isn't uncommon. It requires some diligence when reviewing the backlog, especially for things where a long dependency chain exists to a given date (e.g. Present at Conference requires submitting a proposal, writing the presentation, getting it in by the deadline, travelling there, etc.) I've used different colored stickies to show the story has a time dependency on it, and also tagged with a field/flag to make them stand out
- New opportunities - Does this need to be part of the backlog? Does it get prioritized with other features, or just it "just happen"? Would you ever -not- do this?
Scrum is very good for building up a product, but horrible about managing the "chronic" activities (1-on-1 meetings, department meetings, network with potential customers, etc. all need to happen, but don't "build up" to the final product...) Typically (for me at least :-), things like the burn-up chart are useful to give groups like Marketing the info they need to structure their activities. Some times, if there is a dependency between Marketing and the Dev team, then Marketing might have a story, or sign up for a task. Usually tho, these groups (along with Legal, Finance, HR, Shipping...) don't need to get integrated with Scrum.
My suggestion is use Scrum where it is helpful, and use something else when it isn't.