You mean one basically like this?Why not just use a large standard boring bar. What you are using now is a small Armstrong type of boring bar. Boring bar holders are common for Alores style holders
Could you buy the appropriate size key stock and have a welding shop weld it to the tool holder you want. Have them TIG weld it, it's neater.
Yes , I have a couple of those if interested .There is also this style. Not quite as common but available in the used market. I think Southbend made one as well as Armstrong (or they may both have been made by Armstrong, not sure) and they can take a pretty big bar. For bowl turning you probably aren’t as worried about sneaking into difficult spots as much as getting the stoutest and longest bar that you can. This style might be something to consider.