Where to get Polaris Right ascension value from To calculate for example the polaris hour angle I use this formula to calculate polaris hour angle.

τ = θ - α

τ= hour angle

θ= sideral time

α= polaris RA (~ 2h32m)

But where does the α=2h32m come from? Is there a list? Does this change somehow over time?
Is my understanding correct that this is the time where polaris crosses the upper meridian at Greenwich?
There are several published star catalogs that list right ascensions for stars, along with a lot of other almanac-type data.  Wikipedia's a good resource for common stars (e.g. Polaris).

Right ascensions change over time, as stars move through space.  Star catalogs will have a year associated with them, which is the year that the measurement was taken.