Health services research is not embraced by most university psychology departments, possibly because a lot of that work is already being done in schools of social work, public health, and nursing, but also because clinical psychology in the academy often operates as though health delivery systems don't matter. You'll find plenty of people who build their careers on assessment research or even treatment outcome studies with ill defined plans for dissemination (ie, snowball's chance in hell of ever reaching patients out in the community). HSR definitely has relevance for our field, but in my experience people doing this work tend to be working in more interdisciplinary environments such as VAs, AMCs, think tank-type operations, etc. Training opportunities in HSR are probably more common at the post-doc level in those types of environments since disciplinary boundaries are not so rigid.
If you approach this work from a health disparities angle, you might be able to find some additional opportunities. Engagement, attitudes, barriers are all important to understanding disparities based on factors such as age, rurality, ethnicity, social class, etc. But as with any area of specialization, the most important thing is to really nail your fundamentals during doctoral training and get the best training you can get. You might look for opportunities to take electives outside of the department or join organizations that are HSR-oriented, but don't pass up opportunities to work with a solid mentor doing, say, clinical trials just because they don't focus much on the delivery aspect. You might be able to use your interests to your advantage. Let's say your mentor studies treatments for panic disorder and you want to find out more about what happens when you try to deliver treatment in a community-based setting. That's a jumping off point for a number of studies (some of which have already been done).
