pH value of HF, hydrogen fluoride or hydrofluoric acid? I've been looking for a source but I find different results when I try looking for an answer to this.
I'm looking for weight percentages of 1 to 10% HF (~0.5 to ~5.1M) and what their pH values are.
Now Honeywell says that around 5 to 10% it's pH is above 4.4
However if you calculate this using the $K_a$ of $6.8\times 10^{-4}$, you would get about 1.5 pH, which is quite the difference. 
http://www3.imperial.ac.uk/pls/portallive/docs/1/7276108.PDF (Honeywell / imperial university)
This is just an example, because looking for these values online, for the same molar concentration, different answers are given of around pH 1 to 4.5.

So my question is can somebody explain how to properly get the correct pH values, or confirm what they are.

Also, secondary I would like to create a buffer solution with HF having a pH within the range of 4-7 (specific etching chemistry, $\ce{SiO2}$ vs $\ce{HfO2}$, not etching $\ce{HfO2}$). So other options to achieve this from stock $\ce{HF}$ (49%) with standard chemicals is also an option, however $\ce{NaF}$ is not readily available for me (mostly only access to solutions, such as $\ce{NH4OH}$).
I was able to get some rough pH indicators that are allowed in our lab (cleanroom environment). No clue why a supplier like Honeywell has completely wrong data.

Apparently some sources are completely off, doing the calculation based -log(1/H+) gives the correct values in the end, tested for 50, 10, 5, 1 and 0.5%.
for a quick calculation see:
http://www.endmemo.com/chem/phcal.php