Well lets be clear. Its not really easy, and you are not really talking about a “neutron” source as per the link above.
For example 1 watt of neutrons from DD fusion with full T and D burn gives about 25,000 years to convert 1 mole of U238 to Pu239. This assume a 1 to one neutron usage and yield. This could be bumped up with some Li neutron breeding. But not much I don’t think. So you are going to need many kW of power in neutrons alone. This pretty much means that the DD fusion reactor will need to be at break even or better in practice.
Also I said is easy to separate in quotes for a reason. Its easier than separating U235 from U238. But its quite difficult to do without killing personal and generally making quite a mess.
It should be noted that the controls on depleted U is quite a bit more lax than natural U. Th is even less controlled. Americas insistence on using depleted U for armor piercing rounds notwithstanding, its likely that getting a few 10s of kg’s of U238 would be quite easy.
But I stand by my original claim, that something that can fuse B11+H (really really really hard) will work well with plain old DD (just really hard), and pose a proliferation risk. However this is quite a minor risk compared to say a fission reactor. Permits and inspections that suffice for lots of controlled legal “radioactive” facilities would be applicable here. (ie Co60 for various uses such as UHT milk production).
The biggest problem would still be NIMBY.