Can I meet my birth dad?

Our son, adopted from foster care at 2, now 8, has been asking questions over the last few weeks about his bio dad. We have an open adoption with bmom with 2 visits per year. We also have regular visits with his 1/2 brother who is being adopted by another family. During the last month he is starting to ask questions about his bio dad, including asking to meet him. He's asked before, but it was always an isolated conversation. He's asked three times in the last 5 weeks so I know it is on his mind. We're also in the middle of big transition - FD who was with us for 4 year just left and FS who was with us four years ago just came back. DS's bdad has a long history of homelessness and alcoholism. I have said to our son, we don't know exactly where your dad lives. I don't think he has a house or a phone. But I don't think he's ready to hear, "Your dad is probably sleeping under the bench at the park." Anyone BTDT????????