17th and 18th Century New England meetinghouses were regularly built with forty to fifty foot spans and wider, using king and queen posts trusses. Can't lay my hands on proof at the moment, but I think if you check in a book like Kelly's Early Connecticut Meetinghouses (see below), you will find multiple records of spans in the sixties and at least one seventy footer. So, depending on where you live, the technology for long timber frame spans may be as close as the attic of a nearby old church.

There are certainly numerous examples of long span timber trusses with steel rods and fixtures to be found in 19th Century builders guides by authors like Peter Nicholson, Thomas Tredgold, Frederick Hodgson and James Newlands. No implication intended here that this is easy, or that it should be undertaken casually, simply that it has been and can be done (This from a framer who is currently working on the design a 60' span truss).

Author: Kelly, John Frederick, 1888-1947.
Title: Early Connecticut meetinghouses; being an account of the church edifices built before 1830, based chiefly upon town and parish records.
Collation: 2 v. illus., map, plans. 32 cm.
Imprint: New York, Columbia Univ. Press, 1948.
Language: eng
Subjects: Churches -- Connecticut.
LCCN: 48007952