The option people dismiss and should not: pay for the interviews.
A modest amount for half an hour: a voucher, a transfer, whatever is proportionate: changes several things at once:
Reply rates go up a lot, which solves your access problem directly.
You get people who are not doing you a favour, which means they are willing to be blunt. Free interviews are given by nice people, and nice people are encouraging.
You can specify who you want, rather than taking whoever your network produces. This is the thing you actually lack.
It removes your guilt about asking, which is currently stopping you from asking at all.
There are services that recruit participants to a specification, and they are not cheap. For a small number of interviews, doing it yourself and paying individually is affordable.
One caution: paying does not buy you honest answers about whether they would buy: nobody is reliable about that, paid or not. It buys you access and candour about their current situation, which is what interviews are actually for.
And keep asking about the past rather than the future. Paid or free, would you use this produces the same useless yes.