Can paint/hardware stores match stain like they do paint

Have you been in contact with the company that did the original job? I'd certainly say it's their responsibility to fix the problem at no additional cost to you.

As far as the method of fixing the problem, sanding is probably your best option. When I was figuring out how to properly stain test scraps, I made a few mistakes (see this question). Just to check if I could correct mistakes on my actual project, I sanded down the test scraps and re-stained them. Afterwards, I couldn't tell they had been refinished. (Note: I was working with pine - not sure how cedar will react.)

Just make sure whatever sander you use has built in dust collection, or use it in conjunction with a shopvac. You're going to have a lot of dust from the size of those beams.

The finish color is dependent on two things...the stain, and the substrate (well, and some other variables as well...such as application method, length of time before you wipe it, how many coats, etc.). You can't use one stain on two substrates and expect a match anymore than you would expect finding a match with two different stains on one piece of wood.

So, I think the best you can do is stain one using the stain you want, then get scrap wood of the other material and start a trial-and-error process looking for a stain that will result in the match you want.

Alternatively, use the same species of wood for both parts, or consider going for a purposeful contrast between the two woods.