Here's a list of all the issues that I noticed Richard's work in. While we show the covers, Richard also has interior artwork in them. Hat-tip to Scott Stewart who first found this resource for the issues.
3:3: Summer 1986 - https://archive.org/details/CAT82764316026
3:3: Summer 1986 - https://archive.org/details/CAT82764316026
3:4 Holiday 1986 - https://archive.org/details/CAT82764316027
4:1 Spring 1987 - https://archive.org/details/CAT82764316028
4:2 Summer 1987 - https://archive.org/details/CAT82764316029
4:3 Fall 1987 - https://archive.org/details/CAT82764316030
4:3 Fall 1987 - https://archive.org/details/CAT82764316030
4:4 Winter 1987 - https://archive.org/details/CAT82764316031
5:1 Spring 1988 - https://archive.org/details/CAT82764316032 (internal illos)
5:2 Summer 1988 - https://archive.org/details/CAT82764316033
5:3 Holidays 1988 - https://archive.org/details/CAT82764316034
5:4 Winter 1989 - https://archive.org/details/CAT82764316035
6:1 Spring 1989 - https://archive.org/details/CAT82764316036
6:2 Summer 1989 - https://archive.org/details/CAT82764316037
6:3 Holidays 1989 - https://archive.org/details/CAT82764316038
7:2 Summer 1990 - https://archive.org/details/CAT82764316041
7:4 Winter 1990 - https://archive.org/details/CAT82764316043 (page 15)