Sources and resources.

Urquhart

Project Gutenburg:

Gargantua and His Son Pantagruel 

Wikisource:

The First Book (Gargantua)
The Second Book (Pantagruel)
The Third Book (The Third Book)

Google e-book:

The works of Sir Thomas Urquhart of Cromarty, knight

Includes:
Epigrams, Divine and Moral (1641)
Trissotetras (1645)
Pantochronachanon, or a peculiar promptuary of time (1652)
The Jewel (Ekskybalauron), or the discovery of a most exquisite jewel (1652)
Logopandecteision, or an introduction to the universal language (1653)
Proquiritations

Other:

Logopandecteision online (HTML) here

Rabelais

Online

WF Smith's 1893 translation, with copious notes, in various e-versions at archive.org: Vol 1 (books 1-3) and Vol 2 (books 4 -5)
HTML or rtf versions of the Works in French here
Wikisource has some of Rabelais' works in French here.
The First Book (Gargantua) in French free for Kindle here.
The University of Virginia Library has digital facsimiles of very, very early editions of Rabelais here, and recommendations for further reading here.

Offline

The Complete Works of Francois Rabelais, translated from the French by Donald M. Frame. It's a textbook, so I found a second-hand copy fairly easily.

Second degree sources  

A Dictionarie of the French and English Tongues, Compiled by Randle Cotgrave

Used by Urquhart in translating Rabelais, to the extent that at times the entire English definition from Cotgrave appears in place of one French word in Rabelais.
Digital facsimile, searchable by the French word, here 

Also searchable as part of the LEME (Lexicons of Early and Modern English) here

Mrs Byrne's Dictionary of Unusual, Obscure and Preposterous Words by Josefa Byrne.

Now available as The Word Lover's Dictionary: Unusual, Obscure, and Preposterous Words