If you have to declare any food with Listeria, than any Listeria Spp. food shouldn't be accepted. Even if it isn't the pathogenic type, it is still contaminated with some species of Listeria, so there shouldn't really be an issue with regulations or anything. Legally, if that is how it is phrased, L.spp + has to be reported the same as L.mono +.
The best way I have found to get people to understand is that the only reason something is tested for Listeria Spp. Is to determine if it is possible and/or more likely that it is contaminated with L.mono. Often, when something is listed as L.spp +, it means that they didn't do any testing to determine which it is (When I worked at a food microbiology lab, we would have to ask before confirming it was L.mono+ or - as it was costly. If they did want it to be confirmed, the CoA for that same sample would still say L.spp+ but on a second line it would say something like L.mono confirmation and then + or -, so even if the incoming goods are not L.mono+ so if it only has the L.spp+, you have no idea what species of Listeria it is) If they don't say L.mono, you have no idea if they are or are not. All testing for L.spp does is indicate whether the food could be contaminated with L.mono. If you aren't going to listen to your results, then why even test? The L.spp test is just a cheap way to test for L.mono. Yes, you may have to throw out a bit more if you have to throw out Listeria positive but mono negative contaminated foods, but it's still cheaper than a recall.
If that explanation still doesn't work, you could just tell them you won't accept product that hasn't been tested for L.mono . I would almost guarantee that after they saw the price differences in the species versus mono testing, they would agree to just not accept supplies that has a potential to be deadly for pregnant women, children, and the elderly.
Hope that helps! Let me know if I got too confusing.