I have a lengthy post elsewhere about a canceled Grateful Dead European tour that was scheduled for October 1968. The list of early European tours by West Coast bands seemed relevant here, so I am including it as a separate post
1967-68 European Tours by West Coast "Underground" Bands
Rock touring as we know it today was in its infancy. By late 1968, English bands were starting to come over to America in great numbers, but there was very little action going the other way. Here is a brief survey of European tours prior to October 1968.
England, Netherlands, Germany, Sweden, Denmark
Frank Zappa (then on Verve/MGM) seems to have completed the first European tour by an American band from the West Coast.
The Roundhouse, London, GB
Country Joe and The Fish (then on Vanguard) were flown over for two quick shows. They would return for a lengthier tour in November 1968.
England, Denmark, Belgium, Germany, Netherlands, Sweden
The Airplane (on RCA) and The Doors (on Elektra) had an extensive month long tour that included the Isle of Wight Festival. I believe both bands shared the same booking agency.
Canned Heat September 3-September 30, 1968
England, France, Denmark, Sweden, Germany
In a creative arrangement, Canned Heat (on Liberty) borrowed John Mayall's van and road crew for the English and European gigs, while Mayall in turn used the Canned Heat crew in America. Canned Heat worked with the William Morris talent agency in Los Angeles.
Germany, Sweden, Denmark, France, Austria, Netherlands, EnglandZappa returns for a larger and more successful tour in 1968.
San Francisco's Blue Cheer also did a two week tour of Europe in October 1968, and the San Francisco-based Sir Douglas Quintet toured Europe sometime in the second half of 1968.
Update: I forgot to add a European tour by The Byrds from May 7-16, 1968 (plus a date on June 6 on the way to South Africa). While The Byrds had been to England before, in August 1965, they were still very much a West Coast band. The 1968 lineup featured Gram Parsons and Doug Dillard along with Roger McGuinn, Chris Hillman and Kevin Kelley.
More importantly, I also forgot the November-December 1967 tour by The Electric Prunes, organized by NEMS, Brian Epstein's agency. The Prunes landed at Heeathrow in November and played England and Scotland that month, followed by Amsterdam, France, Denmark and Sweden in December.
The Electric Prunes are often thought to have been from Seattle, because a Seattle dj helped break their first hit, but in fact they were from Los Angeles. They were also a fine live band at the time, immortalized on the Stockholm 67 lp and cd, recorded December 14, 1967 at the Konzerthuset in Stockholm, Sweden for Swedish radio.