Post info about purchasing Pluribasic 6 on any of the forums which Powerbasic users frequent (ie. Jose Roca, PB, etc.). Get a few sales going so you can get some feedback from users. Once you get good feedback of how well it works, then you can consider more extensive methods of advertising PluriBasic.
Just a note about free advertising which few may know about:
Google searches give a high priority to WordPress blogs. Put a WordPress blog on your web site and start writing blog articles about PluriBasic (or any subject potential PluriBasic users might be interested in).
https://wordpress.org/Install the free WordFence plugin to protect your blog.
https://www.wordfence.com/Also get a free account at StatCounter and then follow their directions on how to install a statcounter plugin for the WordPress blog.
https://statcounter.com/Then start writing as many blog articles on your wordpress blog as possible. Use your statcounter account to track traffic to it and see what articles people are reading and write more about those subjects.
You may be surprised at where the traffic comes from. On my blog I have have visitors from the likes of IBM, Microsoft and other big companies.
PS: I found another language you might want to generate code to in PluriBasic. Free Pascal. It supports OLE strings (called AnsiStrings) like Powerbasic and Oxygen do. There is a 64 bit version, as well as 32 bit, so not sure, but it may be able to generate 64 bit apps.