Why would you want one?? I use a one of the brake away straps from sherril's on my 191T and on my 346xp when it goes up. I don't normally use a strap on my 036.
The lanyard that I use is the break away bungee, item number 15278. I have found it to be very user friendly because when you don't want it at full lenght it (I know this isn't quite the right word) retracts so that you aren't getting tangled in it.
you can make them your self.... just get some webbing that has a hollow center. put some bungee cord in it and sew the ends. make a few different lengths if you want.
i read a while back where some one was testing factory sewn slings vs random stiching on a home sewing machine and in a few case's the random stitching held up better than the factory bar tacks. but they never gave out before the factory ones.
Personally, I don't want to be tied to the saw with strong rope. If it ever comes down to something pulling a hung up saw to a breaking point I don't want the breakage to occur in my person my saddle, or ,if avoidable, I'd prefer to not rip the saw frame to pieces. I use 5/16 Hollow braid polypropylene rope for a lanyard. it's light , cheap, easily spliced, and will be the first thing to break in a worst case scenario. Like JPS, I rig it with 2 attachment points.
The bungee lanyards are the best IMHO. The one I put together is the only saw lanyard that I have not nicked with the saw. It gets tangled less in your handsaw and all the other toys you have on your saddle when you have to pass it around your back to make a cut.
I stopped at an "outdoor" type store the other day and saw a really cool way to make the bungee lanyards. They rove the bungee through the hollow webbing, doubled the ends back to form a bight in the bungee and secured it with overhand knots.
all the manufactured saw lanyards i've tried have floppy rings, which really annoys me. so i made me own. the knots are overhand knots with a twist, sort of like beer knots. i make a slit in one side of the tubular webbing, slip the tail in forming a loop, then tie the overhand knot.
the end closer to the ring i girth hitch either directly to the saw (regular handled saws) or to a biner which i clip to the saw (for top handled saws).
with the ring tied as it is it stays very rigid on the webbing, making it easy to grab and clip on and off my belt.