Resources For Learning Southwestern Mandarin (西南官话) We already have:

Resources for learning Mandarin Chinese

Useful resources for learning Taiwanese?

Resources for learning Cantonese

Resources for learning Shanghainese

Resources for learning classical Chinese


Here's what Wikipedia: Southwestern Mandarin has to say about it:

Southwestern Mandarin (simplified Chinese: 西南官话; traditional Chinese: 西南官話; pinyin: Xīnán Guānhuà), also known as Upper Yangtze Mandarin (simplified Chinese: 上江官话; traditional Chinese: 上江官話; pinyin: Shàngjiāng Guānhuà), is a primary branch of Mandarin Chinese spoken in much of central and southwestern China, including in Sichuan, Yunnan, Chongqing, Guizhou, most parts of Hubei, the northwestern part of Hunan, the northern part of Guangxi, and some southern parts of Shaanxi and Gansu.
Varieties of Southwestern Mandarin are spoken by roughly 200 million people. If removed from the larger &quot;Mandarin Chinese group&quot;, it would have the 6th-most native speakers in the world, behind Mandarin, Spanish, English, Hindi, and Bengali.

For a language with so many speakers there seems to be very little resources for learning such a language.
As far as dictionaries go I'm aware of the following:
《四川方言词语汇释》
《成都话方言词典》
《四川方言词典》
《成都方言词典》
《蜀籁》
《四川方言词语汇编》
What resources are available for learners of Southwestern Mandarin?
Michaelyus's answer to a similar question (link in the comments above) is still very useful.  

A general resource that unfortunately may be hard to find now is the 現代方言音庫, a series published by the 上海教育出版社 in the mid 1990s.  This series consisted of a thin booklet titled XX音檔 (usu 100-150 pages) and a good quality cassette for each dialect. The series eventually covered 40 plus dialects, including 成都，貴陽，and 昆明, and the booklets were often written by well-known experts; for example, 成都話音檔 was written by the late 崔榮昌，who did much important work on 四川 dialects. In addition to characters, pronunciation is given in IPA, which I found very helpful.

One problem there may be in making a list of resources for 西南官話 is that it includes a large range of sometimes pretty different dialects.  For example, the varieties spoken in Hubei are sharply different to my ears from 成都 and 昆明.