This article is a brief summary of the current Regimental policy on muskets. It is only intended as an overview and general guidelines. If you have any questions, please feel free to contact Chris Thomas, our CO for more details.
New matchlock  weapons have a preferred barrel length of 36", as it is known that weapons of  this length were actually issued to at least some dragoones. Longer barrels are  acceptable if you want, as there is also evidence of issue of standard infantry  muskets, but there is little evidence for shorter matchlock weapons in our  period, so unless there are physical reasons shorter matchlock weapons should  not be bought new. Wherever possible new muskets should be 12 or 16 bore, as  these roughly equate to the standard and bastard muskets used in the  period.
New flintlock weapons should conform to recognised styles in use  in the period. These could be fowling pieces, with long (probably at least 48") small bore (20 bore) barrels, flintlock muskets (as above), cavalry carbines  (small bore, medium length barrel) or dragons, short and wide bore.
All  muskets should be proofed for at least shot, proof for ball is preferred. This also allows you to live fire if the occasion arises.  
The current  minimum barrel length for SK weapons is 29", measured from the inner face of  the bore to the muzzle.
Gun cabinets which are suitable for the  longer muskets are not easy to get hold of, most being designed for shotguns. I  do not know of any specific current suppliers, although the internet/shooting  magazines will give indications, or it may be worth asking on the (unofficial)  SK site. 
Most wooden powder flasks are probably the ones commonly found on Traders' Row, which are widely used as they are an easy source of wooden flasks.  Personally I think that they are not of  good design either in modern or historical terms!   However, the horn ones  available are probably worse.
Other options include pre-made cartridges  in a pouch or bandoliers of charges. Both of these are actually more  historically accurate than loading flasks for our period.
As far as gun  suppliers I would recommend Albion Small Arms, except that I believe that he is  in the (slow) process of semi retiring, and is not taking any new gun  orders.
At the time of writing we have a batch of guns on order from Albion, and when we get them we may well sell off a few regimentals, so it should be possible for you to buy either one of the new or second-hand ones if that suits. Also remember that we do have these regimental guns, so if you do not wish to purchase at once these are available to borrow, either on an event basis, or if you get a cabinet we can sign one over to you for a more extended period.