Yes. You are as usual right on the money.
Obviously they are not there just to be bought, but I think it is the same grammatical structure.
As far as I know generally this "to be" structure is used in two cases:
1-when something has been planned, almost equivalent to "to be supposed to", as in:
"I am to see the manager.", where a prior arrangement is implied
2-as an equivalent to the for+gerund structure, as in:
"This key is to open the door.", "This coat is to be worn in the summer." where the function of the thing is mentioned.
But with the passive infinitive, this structure might imply possibility. I think the sentence "They are to be bought." falls in the second category, but as the verb is in the passive it implies possibility. "They CAN be bought."
"The animals to be found in this forest are: the squirel, the rabbit..."
is in a way ambiguous:
a-the animals that can be found
b-the animals that are found
But I think (and here I am not sure of what I am saying) when the verb is active this structure shows the function of the noun that is modified. If I say:
A- "The animals to hunt here are the lion and the fox."
I don't think my sentences would mean: "The animals one CAN hunt here are the lion and the fox." Could you just tell me if this analysis is correct of if I am wrong about sentence A?