Ebay and Militaria fairs seem to be the way to get original kit like that. You don't tend to get too many online shops selling original kit.
Having said that a search on google for "Military Antiques" brings up a list of potential antique dealers with online catalogues. I've found one with an M41 jacket here:
http://www.stewartsmilitaryantiques.com ... 7ca5ec7f65
Its a nice cheap $350 
I've got an original M43, although it's a little frayed around the cuffs. Wonder how much that's worth!?
From what ive seen of M41s on Ebay(not that im after one-too expensive)they go for good money and even the tatty ones of which most seem to be as they werent as durable as the later M43s even they are expensive.
There is an ebay seller called HOUNDROBERTS something or other who is i believe a member of the WW2 reenactment forum usualy has quite a few of the harder to find bits of original US WW2 clothing but he certainly isnt cheap 
I've got an original M43, although it's a little frayed around the cuffs. Wonder how much that's worth!?
Cuffs and collars seem to be the norm to wear unfortunately
Before the pound crashed against the dollar M43s could be had for decent money from the States and unless youre a big bloke were quite easy to get hold of-plus they usualy fit QUITE A BIT BIGGER than the stated labelled size due to being part of a layering system.
Platoon in bury does them £45 ish
Well after searching all over I ended up purchasing one off ebay after all!
Your right taffpara some of them do go for a lot of money, I was watching one in the States that was supposedly un issued and was a good size, it went for £315 plus postage!!!!!
I plumped for a more beaten up example so stuck on my bid. Its certainly seen better days but overall it didn't look too bad on the pics and it looks to be a good colour too. I was convinced I would lose out in the final seconds of the auction (tense!!) but in the end I was the only bidder and got it for £35 plus postage so not bad in the end!
Just need to see if it fits now when it arrives!
Good price-too good in fact 
Hope its an original WW2 one and not a post war civvy one,please post some pics up when it arrives or the Ebay number to have a look 
Platoon in bury does them £45 ish
Originals??
As I said its seen better days!
I bloody hope its a proper one now. GGRRRRRRRR!!!!
Ive never owned an original so am not realy qualified to comment on these things but from what ive seen for sale that is a very nice looking one as the cuffs on most are realy frayed as are the collars which have usualy been reversed to cover up the wear/damage.
Was it from the UK or US?
Well my M41 arrived today all the way from Thailand, and oh my god it stinks of curry/Thai food!!!!!
Anyway I would say its deffo an original, you can just tell that its old and of course it has seen some use. Unfortunately for me the sellers measurements were a little optimistic so its a bit on the small side for me but hey ho I didnt plan on wearing it much anyway!
Overall tho I am pleased with it as it seems in fairly good nic in general and the colour is a nice Olivey shade and not too washed out
Bloody hell that was quick delivery
What brand is the zip and have you had a look inside the pockets incase theres an issue label or traces of one?
Oooh, nice original Talon!