It depends on what you’re looking for; as close as the original P10 built in sequencer (Poly-Sequencer 1005), a simple step sequencer for “blip blop” or an advanced step sequencer to more or less replace a DAW:
Any MIDI step sequencer will work and a CV step sequencer will work to control one of the voices as well.
The original built in P10 sequencer was simple and could store 2600 notes (expanded 10 000 notes). I would look at the second hand market for some older similar type of sequencers such Alesis MMT-8 or Roland MC-500 (have one, works perfectly to my P5 and other synths).
A simple step sequencer is, according to my personal preferences, the benefit of a step sequencer to make different simple sequencer loops while tweaking the sound. The Pro One had a beautiful such built in. Doepfer Dark Time (still manufactures) is a such as well as Doepfer MAQ 16/3 (second hand as they are discontinued, have one 16/3 and works great to my P5 as well to my CV controlled modulars).
There are more advanced sequencers at the market such Arturia Beat Step Pro (have one as well as I’m writing from my personal chooses) is simple but still powerful and can easily program MIDI CC, different sequences and drums).
Finally some step sequencers as companion to P5/10 that has my attention: Korg SQ64 and Sequentix Cirklon (wish I had one). Behringer just hinted a possible clone of Arp 1601 with modern features as MIDI (well, that was modern at the mid 80s…) that caught my attention as well.
As said, any MIDI sequencer will work but my advice is to get a simple to operate and you will probably use it more than a super advanced one (a DAW can make that ad well but then you miss the beauty of the hands on experience).