Which of the following are effective approaches when procurement professionals negotiate with monopoly suppliers?

In most commercial negotiations with monopolistic organisations, one can expect that in general they will have far greater bargaining power - you will need them more than they need you. There BATNA is stronger in the short run, but over time their power can be challenged effectively.

Ways of dealing with monopoly suppliers include the following:

Making yourself an attractive buyer

Seeking out alternatives / substitutes in a private or public manner

Designing out the requirement that forces you to go to the monopoly suppliers, or seek to make the product, or threaten to make it yourself if feasible

Lobbying government or campaigning, as part of an industry or trade body, for a reduction in barriers to entry that support the monopoly