Bottom line:  Apart from special populations with known risk for Vitamin D deficiency, there is no evidence regarding practices of Vitamin D screening in general inpatient or outpatient populations.

PubMed search:   vitamin d AND “mass screening”[mesh] AND routine*
This search includes 2 papers published in American Family Physician in 2013.  They present opposing viewpoints on routine screening.  It is probably worth looking at those papers, especially the reference lists.
No papers reported on provider practices regarding Vitamin D screening.

A broader PubMed search of vitamin D and “mass screening”[mesh] seems to address screening in special populations, such as pregnant women, the elderly, and individuals with diabetes.

Web of Science:  Similar results to the PubMed search were found. A recent review presents evidence on Vitamin D screening.

Kulie, Teresa, et al. “Vitamin D: an evidence-based review.” Journal of the American Board of Family Medicine 22.6 (2009):698-706. (cited 33 times)
The last sentence of abstract reads: Unfortunately, little evidence guides clinicians on when to screen for vitamin D deficiency or effective treatment options.

You might be able to use the National Ambulatory Medical Care Survey to determine an estimation of how many patient visits included vitamin D tests, but you wouldn’t be able to tell if they were routine.  There is also a National Hospital Care Survey that might provide similar data; again you wouldn’t be able to tell if they were ordered as a routine or in response to clinical findings or patient history.  If you are interested, we can investigate that further.