You should make it a point to locate out of print issues of Typography Papers, the journal edited by the Department of Typography (and now published by Hyphen Press), and aim to own any issues that are in stock. The level of writing and editing, as well as they object itself, is generally exemplary. See, for example, the 'type rich' issue 7.
In addition:
Visible Language has ocassionally relevant articles. One of the most important for typeface design was 19.1 (1985) with the title The computer and the hand in type design, which is still avaiable on the mag's site; order →here. That issue includes also:
Quarterly Eye occasionally publishes relevant articles. Most back issues are available →here. Some articles are available to read online, such as:
For others, you will need to obtain a hardcopy; e.g.:
Older issues are less easy to get hold of, bt may be locatd on eBay; they contain articles such as:
Eye has a ‘Typography Special’ issue every few numbers. The content in these issues is type-orientated, and therefore interesting. Eye is increasingly confident, and manages to be both British in its approach, and international in its scope and response. Regardless of the typography-special issues, you should consider subscribing.
(Yes, there's lots; these are worthier of your attention:)
Probably the only online resource where every article is of the same, superb, level of scholarship.
Includes a lot of student work. There is a range: try to filter by your reading list.
Several relevant articles. The site has now far too many entries for its structure (authors, titles, etc.), and it is difficult to separate those with broader impact from the lighter ones. Also, no indication of sequence: which are introductory, which are more substantial?
More technically focused, but offered insights into the design process as well. Used to be Thomas Phinney's blog (now at Phinney on Fonts) but is now a joint effort.
Like Typotheque, iLT is beginning to grow too big for its blog format, and the repository of articles / interviews etc. will need some filtering for effective access.