The following has some summarized data (expressed as density plots, not exactly histograms).
https://www.cdc.gov/nchs/data/nhsr/nhsr035.pdf
Depending on what data you want, you might be able to get it from one of the authors, or from the National Center for Health Statistics. The website has public data, but with a quick look I didn't find any on blood pressure.
In theory, data from U.S. Federal Government agencies is for public use, but it may be difficult to find the right person who can give you the data you need.
You might start with the Data Linkage Team, here: https://www.cdc.gov/nchs/data-linkage/index.htm