CCH - nice tune!
there are a bunch of free vst that promise to deliver the "chip" sound, amongt them are those made by odo, who is a hardcore c64 enthusiast. they pretty much all sound the same to me i know about them more from chatting with the developers than using them.. and while i have great appreciation for odo and others work, in many cases they're tainted by their era, eg. people are trying to produce 8 bit sounds using antialiased oscillator tech.. sigh.. ..there is a very, very old vst called "chip32" which i am absolutely certain will alias appreciably
given all of that, i think it would be more astute to implement your own oscillator routines in the code. once you've done it once, you'll see how easy it is to do rather than be dependent on prerecorded audio hereafter.
writing your own audio routine would also allow you to select appropriate settings for the soundcard, instead of eg. recording lofi music to a hifi file then playing it back at hifi rates to depict lofi
perhaps the greater amount of work is not the synthesis but the composition... 8 bit composers develop various techniques to keep the medium interesting, these are reflected in our perception of 8 bit music.. so to produce something appreciably "in style" will take a fair amount of practice to identify and use these techniques.. and may be a great subject for a thread or search..