Applying to History & Philosophy of Science (HPS) PhD programs? History &amp; Philosophy of Science (HPS) is a relatively small field with a handful of PhD programs in the U.S.

Are their any resources on applying to HPS PhD programs and pursing a career in HPS?
HPS isn't a huge subfield of philosophy. I don't know the exact numbers off the top of my head, but I'd guess there are maybe 5 or 6 jobs in the US per year in HPS. It's hard to tell partially because the field is quite diverse. Philosophy of Physics and Philosophy of Social Science are pretty different sub-subfields. So you should try to think about your interests more narrowly. Are you wanting to do philosophy of biology? Philosophy of Neuroscience? Or maybe you're really interested in the birth of modern dynamics at the turn of the 16th century? You need to think about what exactly you're interested in and then find the very best programs you can apply to for that interest. For instance, if you wanted to do Philosophy of Biology, the University of Wisconsin, Madison is a great choice, but if you wanted to do history of physics stuff, the program at the University of Pittsburgh might be stronger for those interests. 

As a first pass, take a look at the Gourmet Report rankings in each of the Phil. Science subfields. But then go through and actually read recent papers by the key faculty at the places that end up high on your list and see whether they're doing the kind of stuff you want to do.

Finally, it would also behoove you to check out the placement data of every school you are considering applying to with a fine-toothed comb. The philosophy job market has been abysmal since 2008. (Not that it was that great before, mind.) So if your ambition is to someday become a philosophy professor, then you should really take a look at whether these schools are managing to place their PhD graduates and if so, in what kinds of places. Investigate the kinds of schools that the graduates land in. Are they the flagship campuses of big state research universities? Are they tiny religious colleges in far flung places? Are they elite small liberal arts colleges? Are they two-year community colleges? You need to really think about what kind of school you'd like to teach at because the experience of being a professor at each of these different kinds of schools is very different. Religious schools pay less. Community colleges and satellite campuses of state schools tend to have heavy teaching obligations. Etc. 

If, like many but not all grad students, you want to end up teaching at a research school with PhD students, you probably would have to get into literally the best program in your subspecialty of HPS to be a competitive candidate.

Good luck.