I think it would be helpful to others if you told us what lathe it is for, post a few photos, and general dimensions. Like spindle ID/OD, cover hole size, how you want it to attache (is your spindle threaded?), how long, and what you plan on using it for. The brass tip spider screws are easy to make, but I can send you a set of 3/8-24 1" Allen or 1.5" cap screw. I prefer to use the fine thread for the spider bolts.
I just have to ask? "I need a spider for my lathe. It would not be practical for me to build one at this time."??
If you need a spider I asume,(usually where I go wrong),that you have a lathe. If you do do you have a drill press as well?
I used a bit of hollow bar which is cheap and available at any steel merchant. As mksj has pointed out they are very easy to make.
Attached are a couple of photo's of mine. I put two rows of set crew locations in it as I often turn Hex bar therefore there is a band of 4 and a band of 3 holes, it just works for what I do. Sorry for the poor quality photo's but I just now walked out and took them and didn't clean up or rig lighting aye.
I wound up using a piece of 2" sch. 40 and some left over mtb bike brake screws to make the spider. I did not want set screws in the lathe spindle or located above the gears so I went with a simple collet. Works great.