Tire Chain Sizing?

So I was looking around for some tirechains today and found that most people didn't carry chains for a 33x12.5" tire... the sizes were all listed as PXXX/XX (or something like that...). We found one brand that made them specifically for a 33x12.5, but they were $200 . Is there a conversion from the 33" sizing to the other format of sizing? That would open a lot more options to me (preferably cheaper options...)

Thanks!

Metric sizes similar to a 33x12.5 would be

315/70r16 which is about a 33.35x12.4
315/65r17 which is about a 33.1x12.4
315/60r18 which is about a 32.9x12.4

Not sure chains would swap from one to the other but the tire dimensions are similar enough you would think they should.