Where to get Official Speed Limit Info

I was ticketed for speeding 55mph on a street with 35mph limit.
I'm thinking about contesting the ticket. First off, that was
a major street with 40mph signs everywhere. I'm hoping to get
an official doc. (presumably from gov.). But where should I do
the search?

Coming back to the ticket. 55mph is more like highway speed.
I'd honest know that if I was travelling that fast. Even if
I was a little above, that was close to midnight on a 3 lane street
with dry pavement (well lited) - that's street traffic was light and it
was safe. I spotted the police car turning
into the same street earlier. Then shortly after, he stopped me.
Could he possibly have enough time to pace my speed? Could he
have mixed his own acceleration (to catch up the distance) with
my speed?

This's my first ticket out of 10 years of driving. Any tips?
Thanks,
Raymond