Does anyone have a chair boneyard resource?  

IKL is correct, if you believe this vintage ad for a variation of your design. The Selig catalog does not list any designer for that model.

Yeah that was what I had always saw, that a variation was IKL. Some suggested to me that Lawrence Peabody actually designed (with heavy influence from the chair pictured) the chair I have, which may be the most common selig lounge import chair, or at least the one I see the most. Also do you have any parts for it! haha.
Reid

If you can't find the part right away, I would say just have one made. It looks like that's a tinted lacquer on the chair, which as far as I know is very hard to touch up. I would strip the chair and have a new part made in whatever wood the chair is made of and then finish it somehow. If it turns out to be two different types of wood, there's always ebonizing...
ETA: I meant if the original turns out to have two different types of wood, which is sometimes the case when tinted lacquer is the finish. Sometimes it's all beech made to look like walnut.

Fwiw, every Selig chair I've seen that has the saddle finish is all beech.

Exactly right, spank. this is the kind of no-brainer that helps keep local craftspersons in business. A piece of beech cut to size, edges rounded over and sanded, four pan-head screws, toned finish, and done. About an hour's labor plus ten $2 bills for materials. It doesn't even need to be perfect, as only toddlers will ever see it.

Having the piece made was my next thought. And I was confused about the wood based on the way it has worn in different areas. Here are a few more photos just to be sure.

Beech, as stated. Strip and sand the chair to bare wood. Leave the seat stretcher as-is for color reference and have someone spray a toned lacquer finish if the original look is what you're after. The traditional DYI stain/finish won't replicate it.
I wouldn't normally recommend it for a valuable piece because it's effectively irreversible, but, ebonizing with permanent india ink, as spanky mentioned, followed with a coat of 1lb.-cut blonde shellac and paste wax is an option for an "updated" look.

I have looked at a Selig catalog that shows an ebonized finish amongst the options. It was the only surprise there. I've never seen a chair done with the finish though. From this I surmise it wasn't offered for long, and wasn't popular at all.

If you decide to refinish the chair, test the finish first in an inconspicuous area with a little nail polish remover on a Qtip. If it's lacquer, it will dissolve almost immediately. If you want to remove this finish, it will come off easily with lacquer thinner or acetone. Once you're down to bare wood you can decide how much, if any, sanding is needed. Unless you love to sand wood, then skip the acetone stripping step and go for it!

RNMB for the scissor chair the bolts you are missing should be the same as the ones holding the legs together. Just pull one out and take it to your local hardware store and have them match the thread pitch. Should be an easy fix. Good luck!

Rip21 that's exactly what I was hoping! Thank you for confirming. And thanks everybody for the input I have friend who is a finish carpenter/cabinet maker who agrees with your thoughts on this! Now maybe if I can catch him when he isn't to busy I can get him to give a hand.
Reid