If you end up going sealed... just get the cheapest sealed box you can find that is the right size and made with 3/4" MDF. Or build your own. If you end up going ported, you'll need some to design and build a custom ported box for your woofer and application. If you go that route, there's many members on here that can do that for you.
Here's a few other woofers I found for sale around here:
http://www.caraudio.com/forums/subwoofer-classifieds/528787-oz-audio-matrix-10s-bnib-dual-2s.html
http://www.caraudio.com/forums/subwoofer-classifieds/532880-2-dd-1510s-w-6-dustcap-vented-enclosure-2.html
Obviously you'd only be looking to buy ONE of the 2 for sale in each thread, but those are pretty good deals. The OZ have a very nice high xmax, and good efficiency, and perform well in small(ish) boxes, asking for about 1.25^ft ported, and half of that for sealed.
The DD are a solid subwoofer as well and at a great price. They've got good xmax and efficiency, not sure on their box requirements though.
For buying a sealed pre-fab, I'd just look around wherever or build it yourself.
sonicelectronix.com will have some.... and other places haha.
Amazon, feebay, etc.
Just saw your edit...
is the a popular site when it comes to boxes? i want a 350z one
therse have a couple 350z ones
http://www.zenclosures.com/350z_s/43.htm
also will i need to take the bass knob out of my old car? or will my indash have a control?
Those boxes look ok, and prices are pretty good. Assuming shipping isn't too bad, that's what I'd go with to keep a clean "oem" look. For a single 10" sub you have 3 options. The cheapest "corner mount" one is not an option because it only offers .43 ^ ft of air space. the other 2 under the strut bar and amp rack one are both viable depending on your preference. the one without the amp rack offer .75^ft of airspace which is good. and the amp rack offers as much as 1.4^ft which should be plenty, depending on your woofer selection you might have to tell them you need less.
As for the bass knob, that's up to you. I don't have one at all, I have no need for it. Depending on your head-unit, you may be able to control it from there as well.