I do see that Helmar is showing they have 1 in stock. PSI may be sending you back to Tennant as I believe they do OE business with them. I do see that GM still lists the 1.6L under their industrial engine options. Impco also has a division in Canada that dresses the GM engines for OE's.
Just seems kind of strange that they are saying NLA as there are a lot more than just sweepers that used this engine.