Daniel Chandler wrote a book Semiotics: the Basics and also supplies an online version here. For a large part of English speaking academia, after Chomsky's reformulation of linguistics into the field that it is today, semiotics became something of a minor topic. At the very least it is not studied in those circles the same way it was studied when Pierce and Saussure were doing their work. That being said, there is still some contemporary work on the subject in English, such as Chandler's introduction. Outside of English speaking academia, semiotics is still a lively field of study, especially in French speaking countries. However, I am a native English speaker with little background in French and I will be unable to help you find those sources.
MIT's Open Courseware program has a lot of lectures on philosophy of language and linguistics. Some of the courses have full lecture notes, some of them have selected lecture notes and unfortunately some of them have no lecture notes. However, all of them list the syllabus for the class which includes the required readings, both papers and textbooks.
You might be interested in Professor Yablo's 2011 course on philosophy of language as well as Professor Holton's 2005 class on the same subject, both of which have lecture notes. Two great textbooks on the subject are Philosophy Of Language by A.P. Martinich and David Sosa as well as Philosophy of Language: A Contemporary Introduction by William G Lycan.
For linguistics, they also have classes on Introduction to linguistics, Syntax, as well as Semantics and Pragmatics. The textbooks and other suggested readings listed on the syllabus should point you in the right direction as well. The Stanford Encyclopedia of Philosophy, which is a great resource for introductions to philosophical topics, has an article on the philosophy of linguistics and it has an exstensive bibiliography containing more references and resources.
The authors that you mentioned are all authors that wrote primary sources on these topics, the textbooks and lectures I've provided are contemporary authors providing commentary and introductions to the primary material. The purpose is to give you a better understanding of what the ideas being presented are so that you can later go and study the primary papers yourself with the tools you need to understand what is being discussed. In this respect, these lectures and textbooks are a lot less difficult to read than the primary sources.
