I wrote successful grant applications for years with the State Department of Health, but other public safety agencies may need to apply through other sources. I believe you need to change your topic, because you don't just need grant writers. You will need to know whether your agency is eligible to apply, and what types of grants are available.
Is the auxiliary separately chartered as a non-profit corporation, or would grants have to channel through the police department? That would pose a major problem if your lead department is vying for the same resources.
Can other government agencies send you their surplus equipment, or does it have to be turned in and go through competetive bid?
As a separate non-profit agency, you may be able to request donations that can then be applied to specific needs, much as in the Cake Walks and other activities engaged in by community organizations. You may wish to find agencies in neighboring communities and ask them how they are obtaining vehicles and resources.
Good luck in your efforts.