i've got a breastgirth i'm happy to sell, full size, dark brown leather, and the front part is black iirc. haven't used it for ages, but it's been saddlesoaped regularly.
otherwise, lots of saddleries have sales on at the moment!
sabre do breastgirths with neckstrap that are reasonably priced. and very good quality
i got my newmarket sheet from a place called oxford hill rugs, where this lady hand makes them, £45 quid, which i thought was good money. proper wool ones aswell, its lovely!
she does post them i think, if you want her number PM me.