I know there are lexan versions. There is a site somewhere with a video of them in action. I cannot quite remember or find it however. These look like a flat ended syringe but I do not know how they functioned.

I have never seen metal ones offered for sale. If you can find a copy of Cache Lake Country by John Rowlands, he has a drawing and description of one based on some metal tubing. Good book too...I have a review here:

http://outdoors-magazine.com/s_article.php?id_article=133