The MegaTraveller Referees Manual has maps of the 1st and 2nd Imperiums. The 1I includes 4 more coreward sectors than the 3I (Windhorn, Meshan, Mendan, Amdukan) but doesn't include the sectors Behind the Claw (Deneb, Spinward Marches, Trojan Reach). It's slightly narrower than the 3I on the Trailing-Rimward edges, but only by a matter of a subsector or two. The map of the 2I is identical to the map of the 1I except it shows Terran Confederation on the rimward edge as a sphere of ~20 Pc diameter centered on Terra. The map of the 2I is also in the CT Solomani alien module, and the map of the 1I is also in the historical booklet that came with the 1990 edition of Imperium (not included in the FFE Games reprint, alas) and DGP's Travellers' Digest issue #5 and Vilani & Vargr (the latter is a dot-map purporting to show every system of the 1I, but its canonicity is pretty dubious -- for instance, the Imperial base-worlds in the Imperium game are NOT part of the 1I per the V&V map!).
Edited to add: I see you're particularly interested in the rimward edges, which is, of course, what I provided least detail about. When I'm home and have the maps in front of me I'll try to provide more exact details (unless someone else beats me to it -- hint, hint).
