There's a list of methods in the following article, including Strike, Cash App, River, BottlePay, Bull Bitcoin, and more. Look for the entries with the ⚡ symbol.

Dollar Cost Averaging. The answer to the question “Is now a good time to buy Bitcoin?” https://cointastical.medium.com/dollar-cost-averaging-the-answer-to-the-question-is-now-a-good-time-to-buy-bitcoin-a84e518f50f0