I'm a teal B2B, and as many on WP can probably tell you, I have had one or two issues with sourcing teal things for my wedding, although since I started planning it has become more popular as a wedding colour so more suppliers are cottoning on.
The best advice I can give is not to get too hung up on a particular shade of teal, as that's what has caused me the most problems. Different suppliers' perceptions of what is "teal" can vary widely, from turquiose blue to jade green.
My BM's dress was actually a prom dress from Debut at Debenhams (which only has a bit of teal in it), but I believe a lot of the main bridesmaid dress designers now offer teal. Her facsinator and handbag have also come from Debut, but are actually slightly more jade than I would have liked (but I would have lost it trying to match perfectly).
Ribbon has been a huge issue. The only ribbon I could find that was anywhere near what I considered to be teal was "Anita's everyday ribbon", which is a 1cm grosgrain. I'm currently awaiting some organza ribbon from eBay which is allegedly teal, but so far I haven't found a satin ribbon that comes near. Everything is either too green or too blue, but then that's me being picky.
My local suit hire shop (Coes of Ipswich) has recently added a teal cravat and handkerchief to their range, but I don't know which other suit hire companies do (I know that Moss Bros certainly didn't when we were looking). I also managed to get a tie-pin from eBay for my H2B which includes a "teal" crystal, which I believe is Blue Zircon.
So far the only other thing teal that I have is the tealights for my table centrepieces. I got these from a company called Northern Lights who will match the tealight to a fabric swatch for you, but these were delivered to work on Friday and I forgot to bring them home so I don't know yet how close a match they are!
An idea that my florist had was to include some eucalyptus leaves in with my (ivory) flowers, as they have a bluey-grey quality to them which matches in with the teal.
I may have a number of items to sell once I get back off honeymoon, but I don't know if that will be too late in the planning stages for your sister? I do currently have six ordinary ties in teal that I bought as a back-up in case we couldn't get teal cravats, so if she's intesterested in those she can take those off my hands now!
Can't think of anything else at the mo, but don't be afriad to ask.
Actually joined in April 2008 but Hitched wiped my profile on 7th August 2009....