It's actually written on the treasury page
Negative Yields and Nominal Constant Maturity Treasury Series Rates
(CMTs): At times, financial market conditions, in conjunction with
extraordinary low levels of interest rates, may result in negative
yields for some Treasury securities trading in the secondary market.
Negative yields for Treasury ...
FINRA publishes a start-of-day and end of day file containing the symbol and issuer of all NMS securities.
Due to the relevance of these files ...
If you only need end-of-day data then Google or Yahoo finance will should be fine.
If you are looking for intraday data then there are only paid sources. Tickdata.com has good global coverage for tick-level data but it is expensive.
You might try eoddata.com if you only need 1-min bars and higher as they have good global coverage and reasonable prices.
Have you considered storing it by adding the additional fields ('level' or 'depth') and ('type'), then you can have a table which looks like this;
time size price depth type
xxx 100 100.03 1 bid
xxx 2000 100.025 2 bid
xxx 0 100.02 3 bid
xxx 33 100.035 1 offer
xxx 45 100....