I'm still having problems locating these items. Xerxes kindly provided the name of interscrew (Chicago bolts) which opened up a new search area. I located a source in New Zealand but they only seem to deal in bulk orders. My interscrews are brass domed and slotted heads on both sides. Still...
I purchased a teak garden table and chairs a while back. Unfortunately a number of the bolts that connect the chairs, and act as pivots when the chairs are folded, have broken and need replacing. The original company seems to have gone out of business. I can best describe these bolts as brass...