Not sure about your local rules, but under the FAR, response time will not justify you as a sole source vendor without additional justification.
Generally, the contracting officer should have to run a "sources sought" solicitation before getting authorization to issue a non-competitive sole-source award. FAR requirement is "(6) A description of efforts made to ensure that offers are solicited from as many potential sources as is practicable, including whether a notice was or will be publicized as required by Subpart 5.2 and, if not, which exception under 5.202 applies."
All these rules are set up to foster competition between vendors, not to stifle it. That being said, people still try to circumvent the fair competition rules with varying degrees of success.
Now if you can get the contract award based on "best value" and not lowest price, you'd be onto a way to differentiate yourself.
Including a service provision where you promise to be on-site within "x" hours of a emergency service call might be enough to qualify you as a "sole source", if nobody else can meet that specification.